Okay, this is the strangest bug I've ever come across, mainly due to its inconsistency. Anyways, here it goes. I believe Hammer is corrupting vmf files. This has happened to two distinct maps now, so I'm not sure what else to think. Here's what I've discovered so far: It causes world geometry to cease functioning. This is the main issue, as it does this seemingly at random each time I compile it. To get this out of the way, yes I AM SURE the geometry in question are not func_detail or any sort of brush entities. I do not have group ignore enabled. They do not have transparent textures on any face. They are not carved monstrosities or concave. The pointfile shows entities leaking through solid, 6 face rectangular geometry. I've tried cordoning the entire map to stop leaks to the void, which produced one compile log free of errors according to Interlopers(except for that skybox error on every TF2 map). I noticed in game that a few world geometry were missing, so I went back to hammer and replaced nodraw on world geometry with an opaque texture so I could easily identify the problem geometry in-game. Yet, the next compile log shows an areaportal leak, even though I made absolutely no other changes to the map. I loaded the pointfile, which shows an areaportal face leaking... TO THE EXACT SAME FACE:bored:. While I was in game on the error free compilation, there were some rather strange particle errors(the console showed that the particle table was full); when I fired the scattergun a bunch of red X's appeared instead of the regular bullets or muzzle flash. Strangely, most other particle effects(on the map and weapon based) worked. And perhaps the strangest part- If I copy the map exactly, piece by piece, into a fresh file, the errors stop for a few compiles, but eventually return. The compile logs before this error begins occurring show nothing strange in them- in fact, earlier I made a point of fixing the zero child area patch and node w/out a volume errors just in case they were the cause. I'm considering hiding areaportals and compiling so I can search for problem geometry in-game, but at this point I'm not sure that will solve anything if areaportal faces can leak to themselves . I've reinstalled Source SDK, as well as A Boojum Snark's Mapping Resource Pack, but it still persists. So, thanks for reading through this wall o' text, and let me know if you have any ideas.