Spawn cubes miss east & west targets

The spawn cubes spawned by the monster spawner will miss the monster spawn spot if the spot is directly east or west of the spawner.

Details
Missed spawn cubes flying directly due east or west will carry on until the game or level ends, even sailing through the walls of the level and eventually wrapping around to the other side of the map. Given enough time, this will result in an endless string of spawn cubes crossing the level (or multiple such streams in case there are multiple monster spawners and/or spawn spots arranged in this fashion).

None of the original commercial Doom games exhibit this bug in their levels.