**People with Custom Permissions are able to change their Gamemode AUTOMATICALLY** EXPLOIT

When you give any player custom permissions, no matter what permission it is (obviously not Operator) , they are able to go into "Settings" and to change their "Personal Gamemode". I checked and you are not able to do this as a "Visitor" or Member". It only happens when "Custom" Permissions are given. This lets players go into creative and fly around my survival based world. It has became a major problem to me and seems like a major exploit. Please fix this. Ty! <3