If you're playing htf for example. and you change mode to DM using /gamemode , the flag stays on the server, no matter how many times you change maps. I tried this on both my own personal , and on a dedicated selfkill server ;E ...

Also, the map list doesn't change as the game mode changes. So if you're playing on your own personal server, and the first mode you played was htf, you can only put on htf maps from the menu..