OneChipMSX - Compatibility with Musical Memory Mapper

On the Compatibility list (page 15 of the Musical Memory Mapper Documentation) it is written that the OneChipMSX is not fully compatible with the Musical Memory Mapper (MMM). The Memory Mapper works but not the SN76489. I wonder what the reason is. Does the cartridge port not provide the necessary voltage? Is v1.3 of the MMM incompatible, too?