diff --git a/src/ui.js b/src/ui.js
index d411bac5..18e2e82a 100644
--- a/src/ui.js
+++ b/src/ui.js
@@ -34,9 +34,6 @@ if (window.Javatari) Javatari.AUTO_START = false;
 var PRESETS; // presets array
 var platform_id;
 var platform; // platform object
-var originalFileID;
-var originalText;
-var userPaused;
 
 var toolbar = $("#controls_top");
 
@@ -80,6 +77,19 @@ var TOOL_TO_SOURCE_STYLE = {
 }
 
 var worker = new Worker("./src/worker/workermain.js");
+
+var disasmview = CodeMirror(document.getElementById('disassembly'), {
+  mode: 'z80',
+  theme: 'cobalt',
+  tabSize: 8,
+  readOnly: true,
+  styleActiveLine: true
+});
+
+var originalFileID;
+var originalText;
+var userPaused;
+
 var editor;
 var current_output;
 var current_preset_entry;
@@ -92,13 +102,6 @@ var compparams;
 var trace_pending_at_pc;
 var store;
 var pendingWorkerMessages = 0;
-var disasmview = CodeMirror(document.getElementById('disassembly'), {
-  mode: 'z80',
-  theme: 'cobalt',
-  tabSize: 8,
-  readOnly: true,
-  styleActiveLine: true
-});
 //scrollProfileView(disasmview);
 
 var currentDebugLine;
@@ -107,7 +110,15 @@ var lastDebugState;
 
 var memorylist;
 
+function deleteEditor() {
+  if (editor) {
+    $("#editor").empty();
+    editor = null;
+  }
+}
+
 function newEditor(mode) {
+  deleteEditor();
   var isAsm = mode=='6502' || mode =='z80' || mode=='verilog' || mode=='gas'; // TODO
   editor = CodeMirror(document.getElementById('editor'), {
     theme: 'mbo',
@@ -188,8 +199,8 @@ function loadFile(fileid, filename, preset) {
     if (text) {
       loadCode(text, fileid);
     } else if (!text && preset) {
-      if (filename.indexOf('.') <= 0)
-        filename += ".a"; // TODO?
+      if (platform_id == 'vcs' && filename.indexOf('.') <= 0)
+        filename += ".a"; // legacy stuff
       console.log("Loading preset", fileid, filename, preset);
       if (text.length == 0) {
         console.log("Fetching", filename);
@@ -215,9 +226,10 @@ function loadFile(fileid, filename, preset) {
   });
 }
 
+// can pass integer or string id
 function loadPreset(preset_id) {
-  // TODO
-  var index = parseInt(preset_id+"");
+  preloadWorker(preset_id); // TODO: what if multiple files
+  var index = parseInt(preset_id+""); // might fail -1
   for (var i=0; i<PRESETS.length; i++)
     if (PRESETS[i].id == preset_id)
       index = i;
@@ -231,13 +243,7 @@ function loadPreset(preset_id) {
   }
 }
 
-function gotoPresetAt(index) {
-  var index = (index + PRESETS.length) % PRESETS.length;
-  qs['file'] = PRESETS[index].id;
-  gotoNewLocation();
-}
-
-function gotoPresetNamed(id) {
+function reloadPresetNamed(id) {
   qs['platform'] = platform_id;
   qs['file'] = id;
   gotoNewLocation();
@@ -385,7 +391,7 @@ function updateSelector() {
   populateExamples(sel);
   // set click handlers
   sel.off('change').change(function(e) {
-    gotoPresetNamed($(this).val());
+    reloadPresetNamed($(this).val());
   });
 }
 
@@ -1299,7 +1305,6 @@ function startPlatform() {
   PRESETS = platform.getPresets();
   if (qs['file']) {
     // start platform and load file
-    preloadWorker(qs['file']);
     platform.start();
     setupDebugControls();
     loadPreset(qs['file']);
@@ -1311,7 +1316,7 @@ function startPlatform() {
     // try to load last file (redirect)
     var lastid = localStorage.getItem("__lastid_"+platform_id) || localStorage.getItem("__lastid");
     localStorage.removeItem("__lastid");
-    gotoPresetNamed(lastid || PRESETS[0].id);
+    reloadPresetNamed(lastid || PRESETS[0].id);
     return false;
   }
 }
diff --git a/src/worker/workermain.js b/src/worker/workermain.js
index e0bec20d..c78df732 100644
--- a/src/worker/workermain.js
+++ b/src/worker/workermain.js
@@ -163,12 +163,6 @@ function wasChanged(entry) {
   return entry.ts > buildstartseq;
 }
 
-/*function anyFilesChanged() {
-  for (var key in workfs)
-    if (wasChanged(workfs[key])) return true;
-  return false;
-}*/
-
 function populateEntry(fs, path, entry) {
   fs.writeFile(path, entry.data, {encoding:entry.encoding});
   fs.utime(path, entry.ts, entry.ts);
@@ -229,6 +223,18 @@ function staleFiles(step, targets) {
   return false;
 }
 
+function anyTargetChanged(step, targets) {
+  if (!step.maxts) throw "call populateFiles() first";
+  // see if any target files are more recent than inputs
+  for (var i=0; i<targets.length; i++) {
+    var entry = workfs[targets[i]];
+    if (!entry || entry.ts > step.maxts)
+      return true;
+  }
+  console.log("unchanged", step.maxts, targets);
+  return false;
+}
+
 function execMain(step, mod, args) {
   starttime();
   mod.callMain(args);
@@ -623,7 +629,7 @@ function linkLD65(step) {
     putWorkFile("main.map", mapout);
     putWorkFile("main.vice", viceout);
     // return unchanged if no files changed
-    if (!staleFiles(step, ["main", "main.map", "main.vice"]))
+    if (!anyTargetChanged(step, ["main", "main.map", "main.vice"]))
       return;
     // parse symbol map (TODO: omit segments, constants)
     var symbolmap = {};
@@ -830,7 +836,7 @@ function linkSDLDZ80(step)
     putWorkFile("main.ihx", hexout);
     putWorkFile("main.noi", mapout);
     // return unchanged if no files changed
-    if (!staleFiles(step, ["main.ihx", "main.noi"]))
+    if (!anyTargetChanged(step, ["main.ihx", "main.noi"]))
       return;
       
     var listings = {};
diff --git a/test/cli/testworker.js b/test/cli/testworker.js
index 97b57dc7..7f62f9f8 100644
--- a/test/cli/testworker.js
+++ b/test/cli/testworker.js
@@ -165,6 +165,7 @@ describe('Worker', function() {
     ];
     doBuild(msgs, done, 8192, [1,1], 0);
   });
+  // TODO: doesn't fail
   it('should not build unchanged files with CC65', function(done) {
     var m = {
         "updates":[