Well, this has already been run twice in a short time frame because of supposed irregularities in the first vote. I'm sure if they get on the blower to Lib Dem HQ they could come up with a reason.
It was an election, not a referendum. Two different things. Though, guessing by what you said, you're cool with voting fraud even where the Austrian Constitutional Court found clear proof of the electoral laws being broken. But hey, that's democracy, one side wins, the other has to shut up, yeah?