Item Order plugin does not change collection thumbnail

In (at the very end in the section "Edit a Collection", it's implied that the Item Order plugin can be used to change which item's thumbnail is displayed in the collections overview page (i.e. /collections/browse).

Is that correct? Because it doesn't seem to be working in my hands. Changing the item order does indeed change the order of the items in /collections/show/NNN and /items/browse?collection=NNN, but the thumbnail in /collections/browse remains that of the most recently added item. I even upgraded to the latest version of Omeka and Item Order, and the behavior hasn't changed...

Any ideas?

Thanks in advance,