This is a trivial bug of HM8.0 encoder.

Before encoding a new tile, all the variables of RD cabac coder are reset, except m_fracBits. It may have very very small impact on coding results, but fixing it will ensure the intention of independent tile.

it's proposed to modify
<line 69, TEncBinCoderCABAC.cpp>
Void TEncBinCABAC::start()
{

m_uiLow = 0;
m_uiRange = 510;
m_bitsLeft = 23;
m_numBufferedBytes = 0;
m_bufferedByte = 0xff;

}

to

Void TEncBinCABAC::start()
{

m_uiLow = 0;
m_uiRange = 510;
m_bitsLeft = 23;
m_numBufferedBytes = 0;
m_bufferedByte = 0xff;

#if FAST_BIT_EST

m_fracBits = 0;

#endif
}