MPDCH is 3GPP-standard, not Ericsson’s. It does mean Master PDCH, in opposition to the Slave PDCH (or just called “PDCH”)
As per today, a MS is not able to listen to a BCCH timeslot and a MPDCH timeslot at the same time.
The reason why they’re not able to do it, i don’t know… that’s the way it is 🙂 Perhaps there are some inconsistencies in the 3GPP, that makes it too complicated to implement ?