View display doesn't stay selected

Hi, I'm having a strange problem with selecting a view display on vocabularies and terms.

I've created a clone of the taxonomy/term view, and selected it in the vocabulary. I edit the vocabulary I want to use the view, select the view in the first drop down, select the view display from the second, ensure the override box is ticked and save.

However, when I go to the taxonomy vocabulary page I see that it's not displaying the right view. When I go back into the edit page the right view is still selected, but the view display has defaulted back to the top of the list. The override box is ticked.

Any ideas as to what's happening? I've tried uninstalling and reinstalling the module, deleting and recreating the views and creating new vocabularies, but I still can't get it to work.