I have an issue where I have been able to bet over the maximum listed amount available to be on a match. Usually if there is a $1,000,000 Limit on the bet, I have been able to bet 2,000,000, 3,000,000, 5,000,000.
You have to put the exact number (for a time I would just type any 7 digits into the betting to ensure a max bet was placed, doing that resets to the default maximum). However if you get the notification that you placed a max bet, then type 2,000,000 into the betting amount, it will allow you to bet that amount.
I do not have it 100% reproducible at the moment except to make it $2,000,000. You are able to do that on any fight that has as a Maximum wager of $1,000,000.