Hi,

Please find attached a simple project demonstrating the issue we are having in our application.

The demo consists of a XamRibbonWindow containing a Ribbon with one ComboEditorTool within it.  There are two buttons for "Add Item" and "Clear Items".

The ComboEditorTool's ItemsSource is bound to an ObservableCollection of String.  The "Add" button adds an item to the collection, the "Clear" button clears all items from the collection.

1. Run the app and press "Add Item".
2. Click the ComboEditorTool and observe "Test 1" has correctly been added to the list.
3. Now click "Clear Items" and then immediately click "Add Item", say 3 times.
4. Click the ComboEditorTool once more and it will only show "Test 1" in the list!!

There are actually 3 items in the list - if you adjust the size of the drop-down using the handle in the bottom right corner, the other items will become visible.

Note, if you click the ComboEditorTool immediately after clicking "Clear Items", before clicking "Add Item" 3 times, it works ok.  Opening the drop-down after the items have been cleared resets the height of the popup, but I believe this should happen without having to open the blank popup first!

Regards,

Dave