After saving a property, the indication of drop area's disappears

When a page is opened in /composermode/composer the areas where items from the Toolkit can be dropped are marked with a yellow dashed border. Click on a box with saveable properties, change the property (e.g. number of items to display in a "Latest comments"-box) and save with the button in the properties box. The page is reloaded but the yellow-dashed-areas do not appear anymore.

The same effect occurs when you click away from the homepage, for example to the news page. If a "dropable area" exist there, it is not marked, and no items can be dragged onto it.