Created attachment 164585 [details]
Stack trace from incident

I was attempting a source file tab from one column to another.  I do this all the time, without incident.  But this time NetBeans hung with the CPU pegged at 100% - ie. only one thread, looping hard.  I used jstack to generate a stack trace (attached).  Most threads were blocked, but one was in native drag code, another was in native graphics paint code.  The odd thing was that I did another stack trace a little later and diff'ed the two of them: they were *exactly* the same.  So it's probably confined to one method.