I've finished ED-E's quest and let the FotA upgrade him. After that, it'd get stuck following, never attack, and get it's butt kicked. Similar thing happened with Veronica. Finished her quests and she just either stands at the Hidden Valley bunker not moving or standing at the 188 trading post not moving after I dismissed her and then went back and get her rejoined. So I'm guessing it's unwise to finish any companion's last quest to get their upgrade perk/trait whatever cause it seems to permanently glitch them. I've had to drop Veronica and switch to Boone and Rex. Rex seems to be the only companion where his upgrade quest worked just fine. I'm concerned to get Boone's upgrade quest because he might glitch upon finishing and then having to go and get *another* companion. Granted I don't need to have two companions, but I do want two companions. And it's annoying to have to dismiss them on the ground that they're unplayable and not because I just want a new companion.

My only problem with companions is ED-E having his inventory 'erased' when he goes with someone to get upgraded.