As you may know, this E3M4 linedef
is basically a (likely erroneous) door switch that monsters can use, which closes the attached sector and blocks the rest of the level if you happen to be on the wrong side when it closes.
In vanilla Doom and most source ports this isn't a huge issue because monsters usually pass the linedef without activating it, as the "door" is in most cases already open when they do. However, in ZDoom the monsters tend to activate the linedef regardless of the sector being open or closed. This is a serious issue at least on UV where the area is filled with monsters, and some of them usually pass and activate the linedef while you fight the horde. Thus if you are unlucky enough to back away into the earlier portion of the level and don't know about the problem, you will get stuck.