MPIO DsmGetContextFromSrb return NULL

Recently while testing MPIO DSM, DsmGetContextFromSrb returned NULL in DsmInterpretError though the context was allocated in DsmSetcompletion routine.
MS MPIO doc says “Note that it is possible for this to return NULL.”
From the above note when would DsmGetContextFromSrb return NULL.
Does MPIO decide whether to return NULL from DsmGetContextFromSrb.
Is this behaviour expected or some sort of memory corruption ? Can this context be traced in WinDbg ?