Applying delta write on backup requires old value to be retrieved if it's not present (e.g. when a node has just become an owner). With old replication, the entry is not committed on primary owner until backup confirms the write, and therefore the backup can retrieve the old value.
With triangle, primary owner commits the value ~concurrently to sending the command to backup owner. Therefore, if backup asks for the value, it likely gets the updated value instead of the original.
This would affect any command with LoadType.OWNER, but currently triangle is not implemented by functional commands which have this load type.