PVS-Studio warning V567 for Fennec Media Project

uint32 CUnBitArrayOld::DecodeValueRiceUnsigned(uint32 k)
{
  ...
  while (!(m_pBitArray[m_nCurrentBitIndex >> 5] &
     Powers_of_Two_Reversed[m_nCurrentBitIndex++ & 31])) {}
  ...
}

This suspicious code was found in Fennec Media Project project by PVS-Studio static code analyzer.
Warning message is:
V567 Undefined behavior. The 'm_nCurrentBitIndex' variable is modified while being used twice at single sequence point. MACLib unbitarrayold.cpp 78

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/