Currently, Koha allows for special characters such as $ in the circulation and fine rule matrix. This causes errrors if a circulation rule has a $ in the fines/fees column.
Where do you get an error? When saving the rule?
I think what was meant here was the missing validation on the fields that is maybe partially to blame on the switch to circulation_rules. Before, you couldn't save an amount of 4,00€ in fine, now you can, but it will cause problems down the road.
*** This bug has been marked as a duplicate of bug 33028 ***