IE 7 hangs while shutting down in Vista SP1 with multiple tabs

Hi,

I am working on a BHO where I create a hidden window for every TAB instance
(This is required for my internal use). When I receive SetSite(NULL) for the
TAB (While closing IE) I go ahead and destroy this window. In Vista SP1 on
some occasions (1 in about 100 times) I see that the DestroyWindow() call
hangs and never returns causing IE to freeze. When I look at the callstack I
see that it is hanging inside NtUserDestroyWindow(). I don't see the hang in
XP.
The hidden window is created withouit any parent.

Has anybody has seen this behaviour?

Thanks,
Mahesh