In the mobile app, group membership is displayed in forums for all to see. This can be a problem especially when group overrides are used for accommodation for disabled students on quizzes. Even if the group name does not communicate the accommodation (such as naming a group "1.5 time" or similar), it can easily signal an accommodation.
This is a design feature, I do believe, but I believe it should be considered a bug.
Hopefully we can either change this (remove it) or be able to control it (and turn off displaying the group membership) via administrative settings.