Megalosaurus odd dmg against all creatures(B-mom, Alpha Rex, everything)?

[HighFlyer15]

So during this valentine's day event I went a bit overboard and bred a ton of Megalosaurus.
With imprinting they all get to 20k hp and 540% damage after leveling them all up to about 10k xp. All fine and easy with the industrial grinder. Each of them now does around 400-600 damage(not the ones in the video, though. I don't test the bosses with my best stuff).
Got plenty of good saddles for them. All in the 130 armor range.
Went up against the Easy Broodmother, made sure it was night, and this is what happened.

https://www.youtube.com/watch?v=us7EsEwtBfo

So besides the obvious fail of taking the 10k damage from the Broodmother early on, you can see that I'm doing 517 damage. That's nice. The guy I'm riding isn't imprinted. These are the test subjects without imprinting. The thing I'm sad about is the damage output by my other guys. Look at those tiny 40-80 damage numbers on the Broodmother. That's pathetic D:
Once in a while they do revert back to their normal damage and lay the smackdown on her but it seems to be only when there are minions to chomp on at the same time.
So what is this? A bug? Unmounted feature to keep solo players from doing the bosses alone(this is on a private server, so no 67% nerf to the bosses)?
I don't get it because bringing all of our Rexes in there solo results in her taking full damage from every Rex in her face.

EDIT: This alternate attack is used against all creatures upon further tests. Please fix, WC.

[HighFlyer15]

Just did a test against an Alpha Rex with 3 unmounted Megas and they did the exact same weird small amount of damage instead of their full potential.
I'm guessing the Mega is such an unpopular mount since this hasn't been reported before now.

[Butzebaer]

It's because they try to grapple the boss. It's a shame they do that. =/

[HighFlyer15]

Originally posted by Butzebär:

It's because they try to grapple the boss. It's a shame they do that. =/

And they continue to do this. I hope it gets fixed soon since they're a lot more easy to use on Aberration with it being dark a lot of the time. It happens against all creatures still.

[Nevil]

I confirm. This problem exists.

[Zardimooo]

I also created a bugreport on the official forum. It's an old bug since they were introduced. 90% of the time they try to grab the target, they pick like chicken and drool all other the place. On aberration the version also got this bug, with minor difference it's the only good main dino. (got the same role as the normal rex on other maps) It's really annoying, since even spinos are crap on aberration...