HCT test case execution timing

Hi,

I am using HCT 12.0 on XP SP2 to verify my USB device under Unclassified
Category. On fast test machines (say 2.8GHz, HyperThreaded machine with 512
MB RAM), some of the automated test cases fails stating that device cannot
be found on the bus under proper tree. On repeating the test by selecting
the failed cases individually it passes. The order of failure can vary - for
example if "USB address descriptor" is the first test and it passes, the
next test scheduled, say "USB descriptor" fails. On later repeating "USB
descriptor" by itself, it passes. I can see the same behavior on standard
USB devices too if tests are run on these, say Microsoft Intellimouse.
This seems more like a timing issue where the next test case starts
executing even before the device enumerates and comes up over USB bus.
I have two questions regarding this behavior:
Is this a known behavior in HCT?
Is it acceptable that cases failing, can be run successfully individually
and those logs used for submission?

Regards,
Najas