It seems the "magnet" after a boss fight has a limit to the number of items it picks up. The result? Several engineers lost. Not that the custom guns are that useful (never used one and I'm at lvl 41), but that still sucks.
Started using slow and, after slowing a few enemies until they couldn't do anything (which is kinda lame), disabled it. But now no enemy whatsoever will attack...
There seems to be a small issue : whenever I try to roll to one side and slide quickly in order to kill one more Goliath, I end up dead most of the time. I'm not necessarily sliding at the very last second either.