My colleague Chris Andritzky keeps getting bitten by problems of the Netbeans Debugger. In a multi threaded application, threads are stopped by breakpoints but the debugger does not realize it.
It seems there are two bugs behind this, one in JDK6 and one in the Netbeans Debugger.
The bug is described in Issue 167776. The JDK6 bug is supposedly fixed in Update 16. The Netbeans bug will be fixed in Netbeans 6.8. Chris is going to try Netbeans 6.8 Milestone 1.

Update:
Chris tried updating to Update 16 first. This didn’t help. Updating to Netbeans 6.8 Milestone 1 solved the problem though.