EnterCriticalSection DEBUGCHK in 4.2

I have been porting some proprietary code from Windows CE 3.0 to CE .Net 4.2
and occasionally hit a DEBUGCHK in EnterCriticalSection. Call stack is:-

COREDLL!DebugBreak() line 102 cscode.c
COREDLL!EnterCriticalSection()
MYCODE!MyClass::MyMethod()

DEBUGCHK call appears to be:-

DEBUGCHK(!(DWORD)hTh & 1))

Where hTh appears to be a thread handle. What is the significance of the
LSBit here and how( if at all ) could my code be effecting this

Thanks in advance

Rimmer