!htrace shows no callstack

When I use !htrace -diff in WinDbg to debug a handle leak, I get a lot of handles (probably the ones that are leaking) that do not show a callstack:

What could be a reason for this and what options do I have to debug this further?

Handle = 0x000273e4 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273e0 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273dc - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273d8 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273d4 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273d0 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273cc - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273c8 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273c4 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273c0 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273bc - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273b8 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273b4 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273b0 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273ac - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273a8 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------
Handle = 0x000273a4 - OPEN
Thread ID = 0x00001190, Process ID = 0x0000114c

--------------------------------------

Update: The handle leak seems to be depending on graphic drivers or graphic cards. It starts to leak when I use any form of WPF it only leaks on some Windows XP systems with a certain graphic cards/drivers.

Calls are performed in kernel mode by ZwOpenProcess routine (http://msdn.microsoft.com/en-us/library/windows/hardware/ff567022(v=vs.85).aspx) and not followed by a ZwClose call. Then the handle leaks. You don't see the callstacks because they are only available when calls are performed from user mode (OpenProcess / CloseHandle).

On an XP SP3, it seems difficult to find the culprit. The solution would be to use the 'Object reference tracing' functionality built in the OS, but this path is paved with issues (see http://www.osronline.com/showthread.cfm?link=198302 for further references). Since you found out this issue arises only when a particular video card is present, you can try to contact the vendor or check for a newer version of the driver.