I tapped the XP potion until it showed my character maxed out, the potions run and then stops shy of the XP it is suppose to give me. You can see in the first picture it turns orange and wont let me give more potions, but in the second picture he is not level 40 as he should be.

Also please add an option to give "Max" or any number of desired potions so we don't have to tap it 300 times.