It is the first time I such rule in a sport betting website. Major bookmakers ,especially in the UK which is considered as the country with a lot of small bookies, bet365, betfair, betathome ,bwin ,eurobet, and many others , if the game do not start or is interrupted during gameplay, the bet usually is a VOID.

Anyway it looks like this is not Nitrogensports fault, they have stated it in the rules. I rarely play tennis but it is good to know the rules, as honestly I never read them there, I took them for granted to be the same as 99% of other sportsbooks.