Hey, this happened to me when I joined a server and it is staying with me throughout all gmod servers. When I move it makes objects have a trail, also parts of map is missing and everything is screwed up. Only happened to me, I asked other people if they saw it they said no.
(Black lines in the picture are there, so I can remove peoples names.)
Edit: Fixed! I just had to restart the game. LOL! Sorry for the inconvenience.