PVS-Studio warning V567 for Source SDK

int m_nNewSequenceParity;
int m_nResetEventsParity;

void C_BaseAnimating::ResetSequenceInfo( void )
{
  ....
  m_nNewSequenceParity =
    ( ++m_nNewSequenceParity ) & EF_PARITY_MASK;
  m_nResetEventsParity =
    ( ++m_nResetEventsParity ) & EF_PARITY_MASK;
  ....
}

This suspicious code was found in Source SDK project by PVS-Studio static code analyzer.
Warning message is:
V567 Undefined behavior. The 'm_nNewSequenceParity' variable is modified while being used twice between sequence points. Client (HL2) c_baseanimating.cpp 5301

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/