Automatically wielding picked up weapons in Borderlands

I've only really started playing Borderlands (i'm at level 17) and sometimes when I pick up a new weapon it is automatically wielded by my character even if it's much worse than the one I was currently using. I was wondering if there was a pattern or rule because it seems inconsistent?

One occasion was particularly annoying when I picked up a shotgun with no ammo during a firefight and subsequently died trying to switch guns.

Solution 1:

If I remember correctly, holding the pickup button longer will auto-equip the weapon, pressing it shortly will just pick it up.

Solution 2:

Holding the pick up item while targeting a weapon, granade mod, or class mod, will auto-equip it.
If you're targeting ammo or money, it will pick up every ammo or money nearby but no weapons or mods, so it's context sensitive.

Keep in mind that this will move the current equipped item to the backpack, so in the case of weapons it'll mess up your configuration (you'll need to manually change the slot if you have a particular order for example)