HOA dues responsibility on BUYER

[Dave S.]

Wanted to reach out and understand if this is legal or not for an HOA to do.

Found a short sale property, put it under contract and later (months later) found out that there were almost $20k worth of over due HOA dues.  The HOA was putting this onto me, THE BUYER, to pay! I didn’t sign paperwork stating that was my responsibility...The seller did. Shouldn’t they go after the sellers? 
Can they hold the property sale up for this??? Cause they certainly did. Now the property is foreclosured on and listed for $45k more!  I don’t know how foreclosure works with past due dues, who pays them, are they waived? 
if the HOA purposely dragged their feet to ensure the property got into foreclosure and so that they get paid that’s not right and I’m going to do something about it.