I've seen situations like Laura described, but if the bank accepted your offer, it should not be a concern here.
But changing it to a standard sale should not have any impact on the deal. However, if you had agreed to pay for certain repairs that are customarily sellers thinking doing so would make it easier to get the short sale approved, you might want to renegotiate that condition and make the sellers pay them instead.
As long as this adjustment has not impacted the terms of your agreement there should be no problem. It would appear that the seller has found the funds necessary to pay the difference and bring the sale to a normal sale.
Consult your agent regarding this change and its effect on your agreement.