I know a few users have stated that this is a shady practice or borderline. Well, most gambling sites have it in their terms that if a bug has been found whether it is known by them or not that the bet would be refunded, and not paid out. As Suchmoon points out Roobet also has this written in their terms. Gambling websites are perfectly in their right to wave off any bet that was the result of a bug within the system, and refund the initial bet amount. Instead, Roobet actually paid to the maximum win which I think is the best possible scenario in this.
Actually roobet didn't admit it was a bug but fixed the non-existent bug anyway. And the max win was not displayed if you didn't click on an obscure icon, so basically you could enter $500 and click 36x without being aware of any limitations - what would you expect to happen? In case of a win I would expect to get $18k. So I strongly disagree with roobet's attempts to have their cake and eat it too. They need to be either 100% transparent about limits without digging around and without needing a calculator, or have strict limitations in software, or both.
Legally they're right but I don't think yahoo was planning to sue them anyway. Legal doesn't mean honest however.