Had it bug out on me today. Set it for 11 potions and was planning on making 22 healing potions. I had exactly 22 potion bottles left.
First cast, I got all 11. Was charged correctly.
Second cast, I got 5 potions, leaving me with 6 bottles (even though it said it took all 11 in the combat log) and charged me for 11 potions in both gold and XP.
:-(
Normally I set the number of potions between each cast. This time I didn't. Just a warning to everyone that this may be a problem and just make certain that you reset the cauldron between each use until a DM can figure this out.