Files being checked out automatically

We are having a wierd issue since installing EPDM 2009. It seems that EPDM is checking out referenced files on its own. Take for instance an assembly with 20 parts in it, all in Approved state (no check-out rights). Then a user submits the main assembly and one other part for Engineering change, allowing that user to check out those two solidworks files. When the transition takes place for those two files to be placed in "Pending ECN", EPDM is checking out the referenced files as well, sometimes all 20 parts, sometimes 5 or 6 that have external references to the assembly (mirrored in the assembly or such).

This problem is not specific to any assembly, user or machine, it is occurring across our EPDM installation for all users.

I've checked rights on transitions and states for all users, and nothing obvious there. Our 2008 install never had this issue.

We've tried checking some settings in the Admin tool, like "Try to check out referenced files" and so on, but no dice.

Any one else seen this problem???