Weird PL/SQL Developer bug: stale windows

Today I observed a weird PL/SQL Developer bug. I was quite frustrated and mystified before I discovered it. I was trying to grant privileges to a role, but the privileges weren't having an effect. I eventually discovered that the problem vanished when I opened a new child window. I suppose that the original window somehow got "stale" and no longer was having any effect.

I even found that the same SQL statement executed in the first window had a different error when executed in a new window. So definitely some aliasing or staleness going on.