I reported CWBRN-3948 - "Add MBT To Pool Menu Option Is Always Grayed Out" back in January. It is in Submitted To Development status, but does not appear to be fixed in X1b. I encountered the problem on day one, because one of my templates from 8.5 had it turned on, and I could not turn it off in X1. The feature is there (though inconveniently buried), and it works if inherited from 8.5, but like Grid Resolution > Follow Snap in the PRV (which
will be fixed in X1b), it is inaccessible in X1a.
EDIT (April 10, 2011): When I wrote "it does not appears to be fixed in X1b", I meant that it wasn't on the list of planned fixes as of March 16. but it was in fact fixed at some point for the X1b release.