Shop undo bug losing health [gameplay]

Any time I use the undo purchase button in the shop, my health drops to the point it was at when i made the purchase.

1. return to the fountain with low health
2. make a purchase while health is still low
3. wait until health is higher than at the time of purchase (so like... one second :D)
4. press the undo purchase button
5. Health drops to the lower point.