voiding bets on sets @ retirements?

Yes. "If the stated set is not completed all bets on this market will be void."

thx. for explanation; the sentence you cited is not in the r® paragraph for users using German language, I didn't check the English version

*rules & reg

aha. i thought it was weird that you asked but now it makes sense. I always use bf in english, even though it's not my first language, for reasons like this.

any idea how B W I N is doing it?

1.) 2-way bets: In a tennis match that ends with one of the players retiring, the “2-way” bet is declared valid as soon as the first ball of the match has been played. For betting purposes, the winner is always the player who is declared the winner by the match referee. The same applies to “Doubles” matches.

2.) All other bets that are determined (i.e. the outcome is already decided) at the time a player retires are valid and will be settled accordingly. All bets that are not decided at the time a player retires are void.

so that means set 2 bets are void on retirement in this set as well? Haven't dared to arb on this till now, while match bets rule where fully clear

There is a part 3 which i should have pasted originally, i think that clarifies point 2 that it will be void.

3.) A set/game/tie-break is deemed to have taken place as soon as its first ball has been played but the outcome of the set/game/tie-break is not decided before the set/game/tie-break is completed.

I should add thats just my interpretation, maybe best to ask them directly.