Were you doing testing and found this out? I tried this myself and when testing, I removed a general hours and saw on the mobile app that I could add hours to it so I thought it was a bug as well. However, I realized that after a while, the mobile app only let me use the general hours that were valid. I'd say you have to log out and back in, but even when I did that originally, some hours were still available, but then I did some other things (went to another week of timesheet, went to main menu and went back to timesheets, those disabled hour types were not available anymore.
I haven't figured out exactly what needs to happen to make sure they are disabled in the mobile app, but I'm guessing the combination of logging out and just giving it time (maybe it "syncs" the data), that only the enabled hour types will show.