Seems to affect every huey. Haven't tried the others yet. I've toyed around with it a bit and it seems like the helicopters either fly extremely slowly ( about 60 kph ) and just keep increasing their altitude until they reach max altitude or they just fly straight up. I've been having varied results but nothing has made them fly like regular choppers.
I mostly tested the slick though, and the classname for that I believe is uns_UH1D_m60.
Edit: Just tried the uns_H13_gunship_CAV and it had the same problem. Seems to be with every chopper from the mod. ( have not tested every single one though ).
I played another mod with a similar problem. I'm not sure, but I think they fixed it by adding the choppers to the NATO faction which made them fly like regular choppahs. Don't quote me on that though. I also tried putting a NATO pilot inside of one of the hueys and gave him a waypoint, but it unfortunately it didn't change anything.