Side note to Nibbler & Coppermine devs: the name is indeed named misleading. Reason for that: it is being used for something that was originally intended for something else. When I wrote the bridge manager I originally planned to use the feature as advertized and allow users to decide wether they wanted their post-based groups to be taken into account or not. Post based groups was then (and is now) a feature that resides in SMF for example. There are groups that you get promoted to by the admin or moderator, and there are groups that you automatically member of based on how many postings you have made. In SMF, you can determine for the entire group-based permission management wether the group membership based on post-count will be taken into account or not. I thought that was a good feature to use in coppermine as well, as it would reduce the number of groups displayed on coppermine's groups control panel.
However, it wasn't me who adapted the bridge files to work with the (at that stage brand-new) bridge manager, but mainly Nibbler did that (and you did a great job btw.). However, he misinterpreted the post-based-groups feature for something else: wether to take into account the non-default groups that the end user has created in the bridge app. That's why the switch does work a bit different to how it was originally designed and that's the reason why it is named in a misleading way. That's why I have changed the translation from "Use post-based groups" (cpg1.4.x) to "Use bridge app custom groups" in cpg1.5.x.
Additionally, the bridging documentation that will ship with cpg1.5.x has been improved. I'm convinced though that the bridge manager should have been re-coded from scratch for cpg1.5.x. Due to lack of time this hasn't been done, so let's schedule this task for cpg1.6.x.