That's very interesting. I heal it a lot and have never encountered it. The only bug I am aware of is a bubble landing inside the shield and damaging it. I'll run it later on to see if i encounter it.
I've seen the lignthning land in the bubble if the SC tank a) goes under a shield himself, b) dies, c) jumps back on SC too early or d) gets too close to the shield while circling. D has gotten us once or twice because I usually do a wide circle around and have clipped the FB bubble when it's in front on occasion with the first one and the SC bubble when it's on the front or side part way through my trip around because I wasn't paying close enough attention.