PVS-Studio warning V610 for GameMusicEmu

void Snes_Spc::cpu_write(....)
{
  ...
  if ( ((~0x2F00 << (bits_in_int - 16)) << reg) < 0 ) // 36%
  ...
}

This suspicious code was found in GameMusicEmu project by PVS-Studio static code analyzer.
Warning message is:
V610 Undefined behavior. Check the shift operator '<<. The left operand '~0x2F00' is negative. game-music-emu spc_cpu.cpp 437

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/