I was trying to figure out why GM doesn't work with my plugin and found issue #64
Does this still apply? Is there any way of setting the primary group in GM?
I'm pretty sure I had this working before..

GM implementation for addGroup will check if the player is in the default primary group, if so it will set the players primary group to the new one. If not it will add the new group as a sub-group.

If you remove a group, it will remove it from the player regardless of it being the primary or a sub-group. If the primary group is removed, the player will be reset into the default group as their primary group.

There is not too much of a way to get around this kind of logic as GM handles multi-group very poorly/differently than other plugins. In addition the GM maintainer thinks that his way is better than everyone elses and wont change.

I will not be changing how Vault adjusts GM groups, as the method detailed above is as close to compatible as I can make it given the way GM handles groups.