Bookmakers offering you to bet on sport event are regulated by betting rules and players placing bets automatically agree with them.
Rules clearly regulate rights and obligations of parties, calculation rate, instrument for solving disputes which constantly arise due to various reasons. Each bookmaker is guided solely by them own Terms and conditions and doesn't take into account rules of other bookmakers.
Betting Rules are very similar, but may at times have significant differences in calculation of interrupted matches, differences in individual sports, minimum and maximum sizes of rates, maximum wager price of parlay.
Sometimes there are situations when matches are interrupted for various reasons, and bookmakers have to pay winnings to bettors, cancel bets or mark bets as lost.
It's also important to study Terms and conditions for betting on kind sport which you bet. For example: some bookmakers offer odds for ice hockey match taking into account overtime and shootouts, but others bookies for regulation time. If you previously didn't find out these aspects, you can avoid unpleasant situations.
So, Fifteenth bettors mistake: no knowledge of betting rules.