personally, i think the bubbles dedicated to healing(the ones where you can't take damage) are a waste of time. i only left a bubble with less than full health once in the entire game, and that was going into another fighting bubble, not one of the healers. throughout the game, my tank was a class 2 with, at the end, 2 leech guns and a 3-spread.
death iv, the number there indicates the delay between attacks.
i have noticed a different bug though. the "death dealer" tree for reavers has no effect whatsoever.