Cannot select image in UV Editor?

What are any potential causes for being unable to select an image in the UV Editor, with the mesh in Edit Mode? I’ve been trying to bake stuff, and keep intermittently getting this problem; I’ve just been randomly saving, closing, reopening, deleting datablocks, etc. to work around it.

I open my blend, create a new blank image, ‘Save as’ .TGA, then just ‘Save’ again to be safe, but I can’t select it or either of the two other existing texture images when in Edit Mode.

Whoops! I looked a little further and found how to work around this – but what causes it? Is it a bug?