RAM reads no longer cause X on the data bus:

When a read was triggered (for example setting _ABUS to AB) in the same
cycle as the data bus has a (non-tristate) value, in the next half-cycle
(when C=1), the TriStateBuffer forwarding data from the RAM to the data
bus would already be active, while the data bus still is pulled to the
"old" value, causing X's to occur.