That's not a bug, that's completely intentional. Your magnet has a weight limit of 3. Bullets have a weight of 1, knifes have 2, and guns have 3. If your magnet has reached its maximum weight, it no longer can attract any more objects. Also, the magnet itself doesn't have a hit box, nor should it.
Really, there is no reason to get so upset. I see that you're good at the game, you've now taken my #1 spot (good job!). If you think that something should be changed, I'm open to any suggestions.