Well I don’t know exactly how it happened.
It was the first time I used the “Hivehand” weapon, I was in the level when you must reactivate the cooling system of a nuclear reactor… I fired against a wall, there was some objects near me (like those chromed nitrogen tanks, or whatever is inside), close enough to be touched by the “flying bullets”, and they started to float like there was almost no gravity. I though it was a feature of the weapon, but then I realized every objects in the map had extremely weird physics!
Restarted the game / loaded my latest quick save, and the bug was gone hopefully 
Sadly I cannot reproduce it, but it was funny
Edit: similar to this: https://www.youtube.com/watch?v=p4CgwI9GeJw