According to section 8.5.2 of WD5d3, the scanIdx value for the intra chroma case should be : ScanType[ Log2( nS >> 2 ) ][ IntraPredModeC ].

The corresponding code in HM-5.0 is at line 4494 of TComDataCU.cpp:
uiScanIdx = aucIntraDirToScanIdx[max<Int>(uiCTXIdx-1,0)][uiDirMode];

The code does not match WD5d3, as the corresponding scanIdx value would be : ScanType[ 1 + Log2( nS >> 2 ) ][ IntraPredModeC ].

As a consequence, levels of an intra chroma 8x8 block are always diagonal scanned regardless of IntraPredModeC.

To match section 8.5.2 of WD5d3, line 4494 of TComDataCU.cpp should be:
uiScanIdx = aucIntraDirToScanIdx[uiCTXIdx][uiDirMode];