Lasers looped through portals fail to ever delete their turf overlays ever
Created by: Exxion
Apparently at least some players knew this but never reported it
If you shoot a laser into a single portal, that's fine. But when you shoot a laser into a portal with the other portal placed so that it loops, you get a problem. The overlays never go away, which not only looks weird (there's just a big laser there) but can also cause lag in extreme cases. (Using the teleporter and a portal gun, I shot a bunch of lasers into the same portal loop and pretty quickly racked up over 2000 overlays on each tile between the portals, which caused a substantial framerate drop for anyone nearby. I think this could be done with the hand teleporter plus teleporter base and thus would be possible in-game, but it would be a fair bit harder.)
Luckily, there's a delay between something entering a portal and coming out the other one, or else this would be a much bigger problem.