Question about Upgrade Part Drops.

[sykora]

I've noticed something strange while playing Shadowgrounds, and I thought I should ask if it was a bug or just me:

Whenever I kill any enemy with either the grenade launcher or the laser rifle's secondary fire, none of the enemies drop any upgrade parts - none. Since both these weapons rip the enemies apart as opposed to just killing them, could this have something to do with it? Or am I just incredibly unlucky?