diff --git a/SourceGen/CodeAnalysis.cs b/SourceGen/CodeAnalysis.cs
index 9b50978..932738b 100644
--- a/SourceGen/CodeAnalysis.cs
+++ b/SourceGen/CodeAnalysis.cs
@@ -804,12 +804,12 @@ namespace SourceGen {
             // it around like one.  The E-flag is always carried over from the previous
             // instruction.
 
-            int backOffsetLimit = plpOffset - 128;      // arbitrary 128-byte reach
-            if (backOffsetLimit < 0) {
-                backOffsetLimit = 0;
-            }
             StatusFlags flags = StatusFlags.AllIndeterminate;
             if (mAnalysisParameters.SmartPlpHandling) {
+                int backOffsetLimit = plpOffset - 128;      // arbitrary 128-byte reach
+                if (backOffsetLimit < 0) {
+                    backOffsetLimit = 0;
+                }
                 for (int offset = plpOffset - 1; offset >= backOffsetLimit; offset--) {
                     Anattrib attr = mAnattribs[offset];
                     if (!attr.IsInstructionStart || !attr.IsVisited) {
@@ -824,6 +824,15 @@ namespace SourceGen {
                 }
             }
 
+            if (flags == StatusFlags.AllIndeterminate &&
+                    (mCpuDef.Type == CpuDef.CpuType.Cpu65816 ||
+                        mCpuDef.Type == CpuDef.CpuType.Cpu65802)) {
+                // Having indeterminate M/X flags is really bad.  If "smart" handling failed or
+                // is disabled, copy flags from previous instruction.
+                flags.M = mAnattribs[plpOffset].StatusFlags.M;
+                flags.X = mAnattribs[plpOffset].StatusFlags.X;
+            }
+
             // Transfer the 'E' flag.
             flags.E = mAnattribs[plpOffset].StatusFlags.E;
             return flags;
diff --git a/SourceGen/RuntimeData/Help/settings.html b/SourceGen/RuntimeData/Help/settings.html
index 2b30375..072244a 100644
--- a/SourceGen/RuntimeData/Help/settings.html
+++ b/SourceGen/RuntimeData/Help/settings.html
@@ -273,7 +273,8 @@ improve automatic operand formatting.</p>
 <p>If "smart PLP handling" is checked, the analyzer will try to use
 the processor status flags from a nearby <code>PHP</code> when a
 <code>PLP</code> is encountered.  If not enabled, all flags are set to
-"indeterminate" following a <code>PLP</code>.</p>
+"indeterminate" following a <code>PLP</code>, except for the M/X
+flags on the 65816, which are left unmodified.</p>
 <p>If "smart PLB handling" is checked, the analyzer will watch for
 code patterns like <code>PLB</code> preceded by <code>PHK</code>,
 and generate appropriate Data Bank Register changes.  If not enabled,
diff --git a/SourceGen/SGTestData/20052-branches-and-banks b/SourceGen/SGTestData/20052-branches-and-banks
index db4c8cf..d493663 100644
Binary files a/SourceGen/SGTestData/20052-branches-and-banks and b/SourceGen/SGTestData/20052-branches-and-banks differ
diff --git a/SourceGen/SGTestData/20052-branches-and-banks.dis65 b/SourceGen/SGTestData/20052-branches-and-banks.dis65
index 58e5da9..a23d28f 100644
--- a/SourceGen/SGTestData/20052-branches-and-banks.dis65
+++ b/SourceGen/SGTestData/20052-branches-and-banks.dis65
@@ -1,8 +1,8 @@
 ### 6502bench SourceGen dis65 v1.0 ###
 {
 "_ContentVersion":4,
-"FileDataLength":224,
-"FileDataCrc32":2055368095,
+"FileDataLength":234,
+"FileDataCrc32":1224113674,
 "ProjectProps":{
 "CpuName":"65816",
 "IncludeUndocumentedInstr":false,
@@ -15,7 +15,7 @@
 "MinCharsForString":4,
 "SeekNearbyTargets":true,
 "UseRelocData":false,
-"SmartPlpHandling":true,
+"SmartPlpHandling":false,
 "SmartPlbHandling":false},
 
 "PlatformSymbolFileIdentifiers":["PROJ:20050-branches-and-banks.sym65"],
diff --git a/SourceGen/SGTestData/Expected/20052-branches-and-banks_64tass.S b/SourceGen/SGTestData/Expected/20052-branches-and-banks_64tass.S
index 0b2c03f..af40eb0 100644
--- a/SourceGen/SGTestData/Expected/20052-branches-and-banks_64tass.S
+++ b/SourceGen/SGTestData/Expected/20052-branches-and-banks_64tass.S
@@ -109,14 +109,28 @@ fwdchk  nop
 
 L543280 jsr     skip+$540000
         nop
-        phk
-        plb
-        lda     $544280
-        jsl     $544280
+        rep     #$30
+        .al
+        .xl
+        php
+        lda     #$0000
+        sep     #$30
+        .as
+        .xs
+        lda     #$00
+        plp
+        lda     #$ea
         nop
-        lda     $4280
-        jsr     $544280
-        jsr     ($544280,x)
+        sep     #$30
+        php
+        lda     #$00
+        rep     #$30
+        .al
+        .xl
+        lda     #$0000
+        plp
+        lda     #$eaea
+        rep     #$30
         nop
         rtl
 
diff --git a/SourceGen/SGTestData/Expected/20052-branches-and-banks_Merlin32.S b/SourceGen/SGTestData/Expected/20052-branches-and-banks_Merlin32.S
index dd09f2e..af43dbf 100644
--- a/SourceGen/SGTestData/Expected/20052-branches-and-banks_Merlin32.S
+++ b/SourceGen/SGTestData/Expected/20052-branches-and-banks_Merlin32.S
@@ -103,14 +103,25 @@ fwdchk   nop
 
 L543280  jsr   skip
          nop
-         phk
-         plb
-         ldal  $544280
-         jsl   $544280
+         rep   #$30
+         mx    %00
+         php
+         lda   #$0000
+         sep   #$30
+         mx    %11
+         lda   #$00
+         plp
+         lda   #$ea
          nop
-         lda   $4280
-         jsr   $4280
-         jsr   ($4280,x)
+         sep   #$30
+         php
+         lda   #$00
+         rep   #$30
+         mx    %00
+         lda   #$0000
+         plp
+         lda   #$eaea
+         rep   #$30
          nop
          rtl
 
diff --git a/SourceGen/SGTestData/Expected/20052-branches-and-banks_acme.S b/SourceGen/SGTestData/Expected/20052-branches-and-banks_acme.S
index 9c3c485..f9a2e1c 100644
--- a/SourceGen/SGTestData/Expected/20052-branches-and-banks_acme.S
+++ b/SourceGen/SGTestData/Expected/20052-branches-and-banks_acme.S
@@ -7,5 +7,6 @@
         !hex    3254af163254af7d3254af163254af7d3254ad1732ad1532ad7e32ad7c32ea20
         !hex    1632201732201832207d32207e32207f32eaa200fc1932fc7a32206e32207132
         !hex    206832206b3220743220773280187c19327c7a326c08106c0810dc0810dc0810
-        !hex    7d3254eaea60200e20ea4babaf80425422804254eaad8042208042fc8042ea6b
+        !hex    7d3254eaea60200e20eac23008a90000e230a90028a9eaeae23008a900c230a9
+        !hex    000028a9eaeac230ea6b
         } ;!pseudopc
diff --git a/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.S b/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.S
index cbca746..6b68221 100644
--- a/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.S
+++ b/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.S
@@ -111,14 +111,28 @@ fwdchk:  nop
 
 L543280: jsr     skip
          nop
-         phk
-         plb
-         lda     $544280
-         jsl     $544280
+         rep     #$30
+         .a16
+         .i16
+         php
+         lda     #$0000
+         sep     #$30
+         .a8
+         .i8
+         lda     #$00
+         plp
+         lda     #$ea
          nop
-         lda     $4280
-         jsr     $4280
-         jsr     ($4280,x)
+         sep     #$30
+         php
+         lda     #$00
+         rep     #$30
+         .a16
+         .i16
+         lda     #$0000
+         plp
+         lda     #$eaea
+         rep     #$30
          nop
          rtl
 
diff --git a/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.cfg b/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.cfg
index 49008c6..19491ea 100644
--- a/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.cfg
+++ b/SourceGen/SGTestData/Expected/20052-branches-and-banks_cc65.cfg
@@ -5,7 +5,7 @@ MEMORY {
 #    MEM001: file=%O, start=$440000, size=28;
 #    MEM002: file=%O, start=$44ffc0, size=15;
 #    MEM003: file=%O, start=$2000, size=32;
-#    MEM004: file=%O, start=$543210, size=138;
+#    MEM004: file=%O, start=$543210, size=148;
 }
 SEGMENTS {
     CODE: load=MAIN, type=rw;
diff --git a/SourceGen/SGTestData/Source/20052-branches-and-banks.S b/SourceGen/SGTestData/Source/20052-branches-and-banks.S
index 369aeae..e8ee3e4 100644
--- a/SourceGen/SGTestData/Source/20052-branches-and-banks.S
+++ b/SourceGen/SGTestData/Source/20052-branches-and-banks.S
@@ -130,4 +130,39 @@ fwdchk:
 
 nxt54b:
         jsr     skip                    ;EDIT: set to "skip" label
+        nop
+
+
+; Test the non-"smart" PLP affects on the M/X flags.
+; EDIT: disable "smart PLP" for this project
+        rep     #$30
+        .a16
+        .i16
+        php
+        lda     #$0000
+        sep     #$30
+        .a8
+        .i8
+        lda     #$00
+        plp                             ;smart->long, unsmart->short
+        lda     #$ea
+        nop
+
+        sep     #$30
+        .a8
+        .i8
+        php
+        lda     #$00
+        rep     #$30
+        .a16
+        .i16
+        lda     #$0000
+        plp                             ;smart->short, unsmart->long
+        lda     #$eaea
+
+        rep     #$30
+        .a16
+        .i16
+        nop
+
         rtl