I'm posting this in the hope that someone else has encountered the same issue:
I've got an application open in full-screen (usually Terminal, but it can be any app). When I attempt to switch to PyCharm using cmd-tab (Command-Tab), the menu bar changes to that of PyCharm, but the window in the foreground is that of a different application. I've got to press another series of keys in order to get PyCharm to come to the fore of the window stack (cmd, then shift-tab with cmd depressed).
Initially, I thought this to be an Apple bug, but, of 11 applications I've got open, only PyCharm and Chrome exhibit this behavior.
Switching between PyCharm and other applications that are not fullscreen does not produce this behavior.
OS: Mac OS X v10.7.4
PyCharm: 117.376 (2.5.1)