I got hit with the switch texture problem, too. To fix it, make sure only ONE switch texture is used by the linedef (as in only the lower, middle, or upper texture). If, say, both the upper and lower texture are a switch, then it won’t work.
The linedef actions are indeed a bit of a mess. They were basically iD adding whatever they needed at the time in an ad-hoc manner, which is how we end up with some of the more strange actions like donut. One thing that really helps is to open the vanilla maps in the editor and inspect which actions they use and how they’re set up. I used E1M9 as a reference a few times to figure out how to do certain tricks.
