Certain weapon effects broken after map change

This is an issue that I’ve narrowed down to being a problem with Garry’s Mod itself. I figured it’d either be the Environmental Systems mod or one of the enhanced weapon effects mods I have, but it’s turned out to be something on the game’s side. Everything will initially be working just fine, no visual problems of any kind.

http://puu.sh/6BVqi.jpg

Then, after a map change, this is what weapons start to do

http://puu.sh/6BVDl.jpg
http://puu.sh/6BW2f.jpg

I’ve tried disabling all addons and rebooting the game, but it still does this to the gravity gun, though every other default weapon in Garry’s Mod fires normally. This effects weapon mods like the M9K weapons, and all of it only happens after a map change.

Any ideas about what the problem might be?