As of September 1st, 2014, gambling on K.R. Engineering tables is against the Second Life Terms of Service. If your table receives payment in order to facilitate gambling, you should update your table to a compliant version immediately. Please see our Skill Gaming article for more details.
More than likely, a double payout means you have more than one Prize Server rezzed in the same region (sim). One server works for every game in the same sim, unless you tell the prize server to only listen to a single table. See the Prize Server article for more information.