Losing primary weapon when passing a weapon on the ground

After picking up a primary weapon from a custom weapons drop or crate, I often lose that weapon if I pass an open weapon crate or a weapon on the ground. I'm not sure if it's a setting on my end or if it's a bug? Can you help me please? I often don't even realize I lost my weapon until I'm in the heat of battle and realize I automatically dropped my primary weapon and ended up with a sniper rifle or pistol in it's place.

HELP!