PVS-Studio warning V567 for Snes9x

static bool8 ReadBPSPatch (Stream *r, long, int32 &rom_size)
{
  ....
  while(length--)
    patched_rom[outputOffset++] = Memory.ROM[outputOffset];
  ....
}

This suspicious code was found in Snes9x project by PVS-Studio static code analyzer.
Warning message is:
V567 Undefined behavior. The 'outputOffset' variable is modified while being used twice between sequence points. memmap.cpp 3926

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/