This glitch often happens to pirated copies of PAL and NTCS games, specially if they're scratched by misusage. As a player is on the lower levels of the map were Jim can crawl under ventilation holes, there's a huge chance of jim going into another room. This totally defies physics as he will end up in another room, or floor. It will not cause the game to freeze, lag or an error, just change Jim's location. This glitch is permanent and the only way not to have it is to not crawl under ventilation holes.