tweaked loading custom blocks with user-defined categories

src/gui.js

@@ -4956,10 +4956,22 @@ IDE_Morph.prototype.deleteUserCategory = function () {
 };
 
 IDE_Morph.prototype.deletePaletteCategory = function (name) {
+    var allCustomBlocks = this.stage.globalBlocks.slice();
+    this.sprites.asArray().concat(this.stage).forEach(obj =>
+        allCustomBlocks.push(...obj.customBlocks)
+    );
+    allCustomBlocks.forEach(def => {
+        if (def.category === name) {
+            def.category = 'other';
+            // to do: refresh all block instances
+        }
+    });
     SpriteMorph.prototype.customCategories.delete(name);
     this.createCategories();
     this.createPaletteHandle();
     this.categories.fixLayout();
+    this.flushPaletteCache();
+    this.refreshPalette();
     this.fixLayout();
 };
 

src/store.js

@@ -385,6 +385,7 @@ SnapSerializer.prototype.loadScene = function (xmlNode, remixID) {
     model.palette = model.scene.childNamed('palette');
     if (model.palette) {
         scene.customCategories = this.loadPalette(model.palette);
+        SpriteMorph.prototype.customCategories = scene.customCategories;
     }
     model.globalVariables = model.scene.childNamed('variables');
 
@@ -1221,7 +1222,7 @@ SnapSerializer.prototype.loadBlock = function (model, isReporter, object) {
         }
         if (!info || !contains(
         		// catch other forks' blocks
-        		SpriteMorph.prototype.categories, info.category
+        		SpriteMorph.prototype.allCategories(), info.category
         )) {
             return this.obsoleteBlock(isReporter);
         }