This is such a basic thing, how did QA not stumble into the issue.
EDIT: Setting the vangle value to 0 in the A-10C messes it up even further. M-2000C on the other hand is fine.
I think I managed to fix it. Seems like JSGME hecked up in some way, probably leaving a file behind: I activated all mods, editor crashed; deactivated, editor crashed; did both things again, it works now.
Sorry for the false alarm.
Since 1.5.4 the mission editor is really slow, and hangs up when loading a mission.
EDIT: It also hangs up when trying to saving anything, even a blank new mission. It does save the mission on disk, but all the UI becomes unresponsive and I'm forced to forcibly close the process.
Spawned ground units would not move or activate. It was reported weeks ago and supposedly fixed internally.
I'm mostly interested since it downright breaks a bunch of DLC campaigns.