For no obvious reason, Phrogram's window suddenly stopped refreshing, as in the text window wouldn't refresh. When I brought up the Task Manager to see what the problem was, it said Phrogram wasn't not responding. When I then closed the Task Manager, the lower right corner stayed visible!
I'm running Windows XP, if that helps assess the problem.
There's no well known Phrogram IDE hangs that I know about. So in this case use taks manager to stop it and restart.
Its quite easy to make a Phrogram that will hang if you don't call Wait or DoEvents. This is why http://phrogram.com/forums/p/1989/7151.aspx#7151
The reason you could still see the corner of Task Manger is becuase of how windows works. When an app goes away it sends a message to all the other windows saying "hey the app on top went away you might want to redraw yourself becuase it was over the top of you". SInce Phrogram was hung it never responded to this message so it leave the overdraw.