PVS-Studio warning V512 for ACE

ACE_INLINE int
ACE_Thread::disablecancel (struct cancel_state *old_state)
{
  ....
  ACE_OS::memset (old_state,
                  0,
                  sizeof (old_state));
  ....
}

This suspicious code was found in ACE project by PVS-Studio static code analyzer.
Warning message is:
V512 A call of the 'memset' function will lead to underflow of the buffer 'old_state'. thread.inl 172

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/