Some things, (usually my AR2) can't be un-equipped, only dropped. If dropped, It can only be re-equipped, not taken. If you try to take it, it says you don't have enough inventory space, even if you do.
Without the ability to unequip something, it get's removed/duplicated with an unusable version in your inventory when you log back in.
When you physgun someone, they float along the ground. Not sure if this is a problem with the gamemode though, or something we can actually fix.