There is a bug in the game where in this case tanks, do not take any damage and negate the damage they take from hostile tanks. Possibly this is caused by the game script thinking it is taking too much damage and removing it. But this is just stupid you get cases as shown in the example where 1 tank can take out all your GS and there is nothing you can do about it.
Example:
https://youtu.be/LeELEKBegZA