In chapter 8.6.1 : Derivation process for quantization parameters, the following condition to derive of qPY_prev is incorrect :

"The current quantization group is the first quantization group in a coding tree block row and entropy_coding_sync_enabled_flag is equal to 1." (taking into account ticket #721)

According to entropy_coding_sync_enabled_flag definition :

"entropy_coding_sync_enabled_flag equal to 1 specifies that a specific synchronization process for context variables is invoked before decoding the first coding tree block of a row of coding tree blocks in each tile..."

the condition should be :

The current quantization group is the first quantization group in a coding tree block row of a tile and entropy_coding_sync_enabled_flag is equal to 1.