Rare material drop disappearing off the floor

[Gestalt]

Not sure if this is a bug or game mechanic, but I've had around 4-5 instances thus far (after the most recent patch) in that I clearly see a mob drop one of the red/black cubes that are the rare drops for each planet like morphics or control modules or rubedos, wait around 30 seconds or 1 minute clearing all enemies in the room, walk over to claim it and it's nowhere to be found. Seems to only happen with those rare material drops so far, never ammo or energy orbs.

[JimmyBaz00ka]

Are these shared drops? I've seen them drop but disappear when someone else walks over it.