I've been having this issue as well.
1. I subscribe to workshop item
2. extract using gmad extractor
3. Move map gma file to garrysmod/maps
4. sync web files
5. reboot
Maps work and users can !votemap #, but the xgui keeps removing the maps from the votemap list, and users can't choose from the list what they'd like.
When I go to move one map over into the votemap list, all the other (accepted maps, ttt maps only) move over as well which is how it should be since I disabled all other maps that aren't ttt.
Ideas?