Yes, I know this... It is happening from time to time, sometimes I can ignore it, sometimes I can't. I know this is frustrating. Sometimes it helps for some time to reset the debugger. There's a command for it in the "Run" menu - add a shortcut to the EditorToolbar for convenience.
But quite often, when the debugger is behaving like this, I'll find a BIG bug in my program some time later, and after fixing it the debugger is silent. So, my feeling is: This is an indication of a hidden issue. Look for pointer or thread issues, be prepared for that hard-to-find stuff...