PVS-Studio warning V567 for AssaultCubeReloaded

template<class LINE> struct consolebuffer
{
  void toggleconsole()
  {
    extern int altconsize;
    if(!fullconsole) fullconsole = altconsize ? 1 : 2;
    else fullconsole = ++fullconsole % 3;
  }
  ....
};

This suspicious code was found in AssaultCubeReloaded project by PVS-Studio static code analyzer.
Warning message is:
V567 Undefined behavior. The 'fullconsole' variable is modified while being used twice between sequence points. console.h 12

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