Sportbook rules are outdated. They haven't been adjusted to factor in new baseball rules. If Tampa scored 10 runs top of 6th instead of 1 run, Tampa bettors would be even more outraged. Simply put this is terribly wrong and unfair rule, we all bet the game line not the 5 inning line. I just heard the Mirage isn't graded bets until game is completed. Comps to the Mirage for being fair.
This exact situation happened on June 28th 2007 in a game between the NY Yankees and Baltimore.
At the end of the 7th Inning Baltimore were winning 6-4 then the Yankees scored 4 in the top of the 8th to take an 8-6 lead. The game was then called before the 8th was completed and the books stuck to their rules and reverted back to the end of the last full inning - and graded the game as a Baltimore Win (no action on Totals + RL as usual).
I agree that the rules are outdated but at the end of the day the rules are what they are so the books need to stick to them unless they have a separate rule on their site.
Its one of them situations where there is no way to please everybody and all books will be inundated with complaints whichever way they decided to go - but if their rules state "last full inning" (as most do!) then that is how it needs to be graded regardless of whether it is a World Series game or not...