I spent some time determining that the sample code for ndisprot that is included in the 6001.18001 WDK has a bug in the IRP cancel code. What's worse is that the bug only exists in the directory labeled 5x, not the directory labeled 60.
For some (at least 2) of the samples in the latest WDK's, they made a clean break from the NDIS 5.x and earlier sample code when they wrote the samples for NDIS 6.0. In the NDIS 6.0 sample they wrote the cancel code according to the pseudo code in MSDN. Unfortunately, they didn't back-port those changes/fixes to the sample code in the 5x directory (sample code intended for NDIS 5.x)
My full description/conversation is here: