Problems with outdated configs
A lot of players don't remove old configs when they stop playing Xonotic. Then a new version comes out they download and start it with their old configs and see a lot of things broken.
I suggest implementing some king of config versioning system. Version should be incremented when the game receives some change which may be broken with old configs. Then when a new client is started with outdated configs it should ask the player to reset the configs (one-click) or continue at one's own risk.