Could be great - but has a _major_ bug

First I was really excited about this game. My son wanted to play it all the time and got amazingly good at it. I thought he was becoming a true subtraction wizard ...
However, then I realized that he didnt actually learn any subtraction at all. Instead he just learned to compare two numbers.

Let me explain. For any subtraction problem, the program offers three options.
A, B, C
One of these is right, one is too small, one is too big (except when the answer is 1, then there will be two 1s).

Alright, here is what my 6-year old son figured out:
The middle number, B, is _always_ too small - so never click on it.
Of the remaining two, A and C, one is correct the other is too big. So all you need to do is compare the very left and the very right numbers and click on the lower one. Voila! You get every answer right without ever doing a single subtraction.

I am not sure if this is intential or not, but it gives parents the illusion that their kids get great at mathematics when really they don’t learn much at all. Please fix this! Thanks!

Kilian q about Medieval Math Battle