I think this happens exclusively when the AI mounts vehicles that have the "AI driver is flying" flag checked (these are actually flying vehicles). Once they get on, a lot of times they go insane and just bowl over every friendly in sight. Maybe about half the time they actually guard at my designated firing positions. This seems to be a separate thing from them actually changing allegiances. When it happens, their allies don't shoot them, but they do look at them. Whereas if I change their team index, their former allies actually shoot at them.

At first I thought it was because their vehicles had different team indexes. They did not. I'm out of ideas. Has anyone else experienced something like this? I'm using a portable version of the HEK called Tinyhek, if that matters.