Lol, I just found it: All modded ACUs are missing the AverageDensity parameter.

I noticed that the collision behavior of the modded ACUs in this mod is different than vanilla. In vanilla the ACUs can push other units, like T1 eng, around, but the modded ACUs cant. Even funnier, a T1 eng. can push the modded ACUs around, so the collision behavior is swapped in some kind of way. Does anyone have an idea what could be causing it?

Ha! I found a kindred soul! I just uploaded some of my own small Blackops changes to the vault, to play with my friends and thought why not go and see what's new on the formus. heh
Uhm, do you mind if I incoporate your changes into my own stuff? Especially the bugfixes. but also the balance changes, they look reasonable enough. but I am not intrested in the nomads parts. I'll obviously make sure to credit you and the others.