Seems like it might be client related, it's very odd. Other potions seem to withdraw just fine, only exception being combat potions. The bot will actually recognize the potion in the bank and determine which one it should withdraw, but just won't withdraw it. As for your suggestion, I do intend to improve looting in general, this will not be till at the earliest the first week of May after my finals are over.
Gave you a trial just now. It will pick up looting bag as long as you have it selected with other loot.