Bug with weapon maxing?

I maxed out a weapon for someone while playing on the Mooncraters map, and when I handed it back to him the weapon didn't change. It was a Force +1 Flak.

I lost the 150 adren, but the weapon stayed a +1.

Sorry if this has been discussed before. Just curious about it.

It happened once to me, but the problem was that having picked up the weapon I forgot to switch to it before maxing. So I maxed a different weapon

ops:
It was only when I went to pass it back I noticed it was still not maxed I realised what I had done (or not done)