Marketpress global cart cookie issue

I'm using marketpress and prosites together so marketpress is not network activated and only active on some sites.

Each site's store should be entirely separate from the next however the global cart cookie still appears to be being set.

This is causing problems with, for example, a purchaser on site A seeing pre-populated shipping details from a totally separate purchase on site B. Another reported issue is with orders from two site A users being mixed together so the cart for the second user contains items from the first.

I think the mp_globalcart cookie may be causing the problem here but any insight you can provide on this and, more importantly guidance on how to fix it, would be very helpful.