I think more often then not, an invisable tank, plane, flak gun or aircraft carrier for that matter is more a case of not seeing the one that gets you rather then a bug.
If a tank is shooting at you from a conceled position(in trees,behind grass etc..) he may not be invisable just conceled from your veiw.
I had the same thing happen in reverse to me, one of the L.T.A.R.'s was shooting up a v-base from a patch of woods, I drove out to flank him, I was able to get in very close when i realized that from his point of veiw he couldn't see me due to the woods and in piticular the grass he was hideing in was blocking his veiw, easy kill.
ON 200 ch he claimed i was invisable, until he realized what had happend. his veiw was blocked by the grass, the same grass conceled me and allowed me to see him from the other side.
not to say that there are no "bugs" and that what you saw was not one, just that it's more likely there was a player in tt that found himself a good spot.
Even your best buddys don't share the best spots to pick the biggest strawberrys, I don't think anyone who could make their tank invisable could keep it a secret from HTC.
Some days your the bug some days your the windsheild.