FindFirstFile causes 'TempPte.u.Long != 0' assertion failure when opening Display Properties

Created an attachment (id=5771)
Debug log

I just hit this assertion when opening Display Properties Control Panel.
Possibly a problem with FsRtlIsNameInExpression or FastFat.

Maybe relevant: just previously, I've had an application create a file (inside WM_LBUTTONDOWN), then exit. (This is where the buggy win.cpp debug prints come from ;]).

I've attached the debug log annotated with some raddr2line results.
Running trunk/50816 on VirtualBox 4.0.4, Win7/x64 with a VHD disk regularly written to by Windows (while the machine is not running).

I couldn't reproduce the crash for a second time yet, and will post again if I find a way to do so; if it is indeed an FsRtlIsNameInExpression problem, that shouldn't be necessary though.