Right clicking a group icon in the fixture chooser to update groups causes all the fixtures currently in the group to be selected. Totally screws you up. However, right clicking on a group in a picker window doesn’t select everything in the group. Works correctly in 2.3, currently broken in 3.0.18895.
Thanks for reporting this, I’ve added it as bug 7498
If you change the type of some fixtures in the created group, they are excluded from the group.