Changing amount in Currency Exchange crash.

Bug:
Playing with the amount field on "what I want" causes the game to crash. I crashed multiple times while changing the number to play with the ratios.
The game freezes then it quits out.

How to reproduce:
1)Enter an amount in the "what I want" field.
2)Change the amounts a few times in a row.
3)May crash as well on changing "what I have" field's amount.

I have had success using this system but experienced this bug a few times by now.