BP_ENABLE_MULTIBLOG and Membership plugin

I've got a network of sites (quickscan.nl, bimprotocolgenerator.com, bimserver.org) that all run on myb.im networksite. I've activated 'BP_ENABLE_MULTIBLOG' to share users and other BP content across domains.
For some reason I don't get the Membership plugin up and running on the subsites (bimquickscan.nl, bimprotocolgenerator.com, etc)
Did you guys test this setup? Any hints?