I don't know all of the situation this occurs in, but for my example, I have Find and Structure on the right side of the IDE, pinned open (fig 1.) When I am done using my Find, I close it (with the red X.) In 2.1.5 and before, closing Find would leave Structure open. Now, when I close Find, it minimizes Structure (fig 2.) Has a setting changed or do I need to file a bug?