I don't know about the rest of it with MP, but there has been on going issues with being able to combine items with sellers that are on it.

Most sellers affected are advising buyers to purchase and then the seller will refund the excess post - but pretty sure you will be paying fees on the full postage cost etc.

AFAIK eBay are most certainlly aware of it, in the US the tech advice is they are trying to fix, whether anything is done is yet to be seen.

They are currently rolling out another wave of MP and also beginning the Chinese roll out, so these glitches keep happening and if they don't get a handle on it soon, sellers are going to give up I have no doubt.