No other weapon seems to have this problem.I tried with the Lenz, Zarr, Mutalist Cernos, Dread, Angstrum, Kulstar, and some other weapons. It's just the Bramma that seems to have this issue.
Edit: apparently the Ferrox and Akarius have this issue too.
Edit edit: tyypoo
Hey TBeest! This issue will be fixed in the next mainline.
Edit: I checked the Ferrox and Akarius as well and they also work properly with Magnetize now.