diff --git a/SourceGen/DisasmProject.cs b/SourceGen/DisasmProject.cs
index c9f4674..3c2ab6f 100644
--- a/SourceGen/DisasmProject.cs
+++ b/SourceGen/DisasmProject.cs
@@ -2352,18 +2352,14 @@ namespace SourceGen {
                                         "project/platform symbol");
                                     needReanalysis = UndoableChange.ReanalysisScope.DataOnly;
                                 } else {
-                                    affectedOffsets.Add(offset);
+                                    AddAffectedLine(affectedOffsets, offset);
 
                                     // Use the cross-reference table to identify the offsets that
                                     // we need to update.
                                     if (mXrefs.TryGetValue(offset, out XrefSet xrefs)) {
                                         foreach (XrefSet.Xref xr in xrefs) {
-                                            // This isn't quite right -- in theory we should be
-                                            // adding all offsets that are part of the instruction,
-                                            // so that affectedOffsets can hold a contiguous range
-                                            // instead of a collection of opcode offsets.  In
-                                            // practice, for a label change, it shouldn't matter.
-                                            affectedOffsets.Add(xr.Offset);
+                                            // Add all bytes in the instruction / data item.
+                                            AddAffectedLine(affectedOffsets, xr.Offset);
                                         }
                                     }
                                 }
@@ -2432,8 +2428,8 @@ namespace SourceGen {
                             }
                             Comments[offset] = (string)newValue;
 
-                            // Only affects this offset.
-                            affectedOffsets.Add(offset);
+                            // Only affects the bytes at this offset.
+                            AddAffectedLine(affectedOffsets, offset);
                         }
                         break;
                     case UndoableChange.ChangeType.SetLongComment: {
@@ -2449,8 +2445,8 @@ namespace SourceGen {
                                 LongComments[offset] = (MultiLineComment)newValue;
                             }
 
-                            // Only affects this offset.
-                            affectedOffsets.Add(offset);
+                            // Only affects the bytes at this offset.
+                            AddAffectedLine(affectedOffsets, offset);
                         }
                         break;
                     case UndoableChange.ChangeType.SetNote: {
@@ -2466,8 +2462,8 @@ namespace SourceGen {
                                 Notes[offset] = (MultiLineComment)newValue;
                             }
 
-                            // Only affects this offset.
-                            affectedOffsets.Add(offset);
+                            // Only affects the bytes at this offset.
+                            AddAffectedLine(affectedOffsets, offset);
                         }
                         break;
                     case UndoableChange.ChangeType.SetProjectProperties: {
@@ -2555,6 +2551,31 @@ namespace SourceGen {
             return needReanalysis;
         }
 
+        /// <summary>
+        /// Adds all offsets associated with the code or data item at the specified offset
+        /// to the range set.
+        /// </summary>
+        /// <remarks>
+        /// In the past, it was only really necessary to add the first offset, because that
+        /// would trigger the entire line to be redrawn.  That's not the case with arend
+        /// directives, which are associated with the last byte of a multi-byte item.
+        /// </remarks>
+        /// <param name="affectedOffsets">Range set to update.</param>
+        /// <param name="offset">Offset of first byte.</param>
+        private void AddAffectedLine(RangeSet affectedOffsets, int offset) {
+            int len = 1;
+            if (offset >= 0) {  // header comment doesn't have an Anattrib entry
+                len = mAnattribs[offset].Length;
+            }
+            if (len == 0) {
+                Debug.Assert(false, "Zero-length affected line?");
+                len = 1;
+            }
+            for (int i = offset; i < offset + len; i++) {
+                affectedOffsets.Add(i);
+            }
+        }
+
         /// <summary>
         /// Clears all cached visualization images.
         /// </summary>
diff --git a/SourceGen/LineListGen.cs b/SourceGen/LineListGen.cs
index 8c765f5..7ba2e94 100644
--- a/SourceGen/LineListGen.cs
+++ b/SourceGen/LineListGen.cs
@@ -307,7 +307,8 @@ namespace SourceGen {
                     if (lineType == Line.Type.Code || lineType == Line.Type.Data) {
                         lineType = Line.Type.CodeOrData;
                     }
-                    if (line.FileOffset == curOffset || lineType == Line.Type.ArEndDirective) {
+                    if (line.FileOffset == curOffset ||
+                            (tag != null && lineType == Line.Type.ArEndDirective)) {
                         // Another item at same offset.  We special-case the arend directive
                         // because it's contained within the previous item, so we want it to be
                         // set on the existing [offset,offset+span) range tag.
diff --git a/SourceGen/WpfGui/EditDefSymbol.xaml b/SourceGen/WpfGui/EditDefSymbol.xaml
index b3ccfdc..d45ddbb 100644
--- a/SourceGen/WpfGui/EditDefSymbol.xaml
+++ b/SourceGen/WpfGui/EditDefSymbol.xaml
@@ -32,8 +32,8 @@ limitations under the License.
         <BooleanToVisibilityConverter x:Key="BoolToVis"/>
 
         <system:String x:Key="str_WidthLimitFmt">• Decimal or hex value, 1-{0}</system:String>
-        <system:String x:Key="str_ProjectConstant">Constant</system:String>
-        <system:String x:Key="str_VariableConstant">Stack-Relative Offset</system:String>
+        <system:String x:Key="str_ProjectConstant">_Constant</system:String>
+        <system:String x:Key="str_VariableConstant">Stack-Relative _Offset</system:String>
     </Window.Resources>
 
     <Grid Margin="8">
@@ -54,7 +54,7 @@ limitations under the License.
         <TextBlock Grid.Column="0" Grid.Row="0" Margin="0,0,8,0">Symbol type:</TextBlock>
         <StackPanel Grid.Column="1" Grid.Row="0" Orientation="Horizontal" Margin="0,1,0,12"
                     IsEnabled="{Binding NotReadOnlyValueAndType}">
-            <RadioButton Content="Address" GroupName="Type" Margin="0,0,0,0" IsChecked="{Binding IsAddress}"/>
+            <RadioButton Content="_Address" GroupName="Type" Margin="0,0,0,0" IsChecked="{Binding IsAddress}"/>
             <RadioButton Content="{Binding ConstantLabel, FallbackValue=Constant}" Margin="8,0,0,0"
                             GroupName="Type" IsChecked="{Binding IsConstant}"/>
         </StackPanel>