Index: lams_central/web/includes/javascript/authoring/authoringActivity.js
===================================================================
diff -u -r1a329783c6ff3378add4b1279182e37698058230 -r5be40944bddd2480de5d58417669a56c4d051680
--- lams_central/web/includes/javascript/authoring/authoringActivity.js	(.../authoringActivity.js)	(revision 1a329783c6ff3378add4b1279182e37698058230)
+++ lams_central/web/includes/javascript/authoring/authoringActivity.js	(.../authoringActivity.js)	(revision 5be40944bddd2480de5d58417669a56c4d051680)
@@ -257,6 +257,7 @@
 		this.authorURL = authorURL;
 		this.title = title;
 		this.readOnly = readOnly;
+		this.requireGrouping = false;
 		if (evaluation) {
 			this.gradebookToolOutputDefinitionName = evaluation[0];
 			this.gradebookToolOutputWeight = evaluation.length > 1 ? evaluation[1] : null;
@@ -618,8 +619,10 @@
 										   }))
 						 // activity colour depends on its category ID
 						 .attr({
-							'stroke' : layout.colors.toolActivityBorder[layout.toolMetadata[this.learningLibraryID].activityCategoryID],
-							'stroke-width' : '0.5',
+							'stroke' : this.requireGrouping ?
+									   layout.colors.activityRequireGrouping 
+									   : layout.colors.toolActivityBorder[layout.toolMetadata[this.learningLibraryID].activityCategoryID],
+							'stroke-width' : this.requireGrouping ? '3' : '0.5',
 							'stroke-linejoin' : 'round',
 							'fill'   : layout.colors.activity[layout.toolMetadata[this.learningLibraryID].activityCategoryID]
 						 }),
Index: lams_central/web/includes/javascript/authoring/authoringGeneral.js
===================================================================
diff -u -rdae7eeb158338a956aaec37705b0c1efb18be6f6 -r5be40944bddd2480de5d58417669a56c4d051680
--- lams_central/web/includes/javascript/authoring/authoringGeneral.js	(.../authoringGeneral.js)	(revision dae7eeb158338a956aaec37705b0c1efb18be6f6)
+++ lams_central/web/includes/javascript/authoring/authoringGeneral.js	(.../authoringGeneral.js)	(revision 5be40944bddd2480de5d58417669a56c4d051680)
@@ -132,7 +132,9 @@
 			'optionalActivityBorder'    : '#00007f',
 			// dashed border around a selected activity 
 			'selectEffect'        : 'black',
-			'transition'   		  : 'rgb(119,126,157)'
+			'transition'   		  : 'rgb(119,126,157)',
+			// highlight TBL activities which should be grouped
+			'activityRequireGrouping' : 'red'
 		},
 	
 		'defaultTextAttributes' : {
@@ -1596,6 +1598,8 @@
 		for (var activity of activities) {
 			if (!activity.grouping){
 				activitiesToGroup.push(activity);
+				activity.requireGrouping = true;
+				activity.draw();
 			}
 		}
 		return activitiesToGroup.length === 0 ? null : activitiesToGroup;
Index: lams_central/web/includes/javascript/authoring/authoringProperty.js
===================================================================
diff -u -r1a329783c6ff3378add4b1279182e37698058230 -r5be40944bddd2480de5d58417669a56c4d051680
--- lams_central/web/includes/javascript/authoring/authoringProperty.js	(.../authoringProperty.js)	(revision 1a329783c6ff3378add4b1279182e37698058230)
+++ lams_central/web/includes/javascript/authoring/authoringProperty.js	(.../authoringProperty.js)	(revision 5be40944bddd2480de5d58417669a56c4d051680)
@@ -705,6 +705,10 @@
 					if (newGroupingValue != activity.grouping) {
 						activity.grouping = newGroupingValue;
 						redrawNeeded = true;
+						if (activity.requireGrouping && newGroupingValue != null) {
+							// get rid of red border set by TBL check
+							activity.requireGrouping = false;
+						}
 					}
 				}