As one that's flown the P-39 often (but not often enough for my tastes) I have had a gas leak in one tank MANY times....
It may be the case that when you leave it on auto, that tank drains very fast from the bullet hole, but the other tank drains very fast because you're using it up.
Always (repeat: ALWAYS) switch to the damaged tank, and use as much as you can from that tank before it's gone!
If you have it on film, submit in bugs forum.
EDIT: Please note you only have about 25 mins on full internal gas... that's about 12 minutes when one tank is totally drained. If you upped 50% to begin with, you'd have 6 minutes or less in the "good" tank as the bad tank drains. You may just have not had much gas left over after your bad tank went dry. It happens once in a while.