Hopefully you don't mind this somewhat unorthodox means of reporting bugs. It's nice to know they're not being forgotten, even if they won't be fixed anytime soon. :)
Picking up ammo off the ground reloads all equipped weapons, but does not trigger effects that are triggered by reloading. I believe this is a bug (perhaps an unintentional one), as picking up ammo off the ground should never be detrimental to gameplay.
For a specific example, the 'Papa Pump' shotgun increases damage on a reload and requires you to be close to the enemy (it's a shotgun). If you kill any enemy who drops an ammo pickup, you won't be able to reload Papa Pump after the kill, and don't get the damage boost from its Masterwork effect.