Before you go all legalistic on their asses, you might want to recall that the seller is broke (hence the short sale).
This may not be their fault. It may be that there is a property manager who does not really understand the position he is in and that if there is no short sale, the HOA gets zero. It may be that the first lien holder is stupid and is unwilling to give the HOA any amount of sale proceeds.
I just got a $5400 HOA debt worked out for $3400
$1000 was paid out of escrow and the rest was paid at $200 a month for a year by the sellers. I would have been more aggressive but the sellers wanted to work it out–whatever.
However, a lot of deals get destroyed because an hoa gets greedy or because the agent does not think to bargain.
While not technically legal, you might want to offer to cover some of the amount and work it out directly with the HOA. It sucks but if a few thousand would allow you to complete a purchase of a few hundred thousand then it might be worth considering.
Good luck and feel free to ask me any questions here or directly