Don, a home that has an "Open Permit" is one where the owner (or owner's contractor) has "Opened" a building permit....maybe a demolition permit, an electrical permit, a plumbing permit...whatever the case may be, they started the renovation out correctly by "Opening a Permit".
BUT...since it's a short sale, that indicates that they ran into a hardship and can no longer afford to complete the renovation...therefore, they cannot "Close the permit" with the city. So, anyone purchasing the home will be required to complete the renovation and "Close the permit" themselves.
The answer to your question, "Do you think it is OK to buy?" depends on a lot...actually, A LOT more! Hopefully you have a trusted Real Estate professional, a good Home Inspector, a qualified Lender and Title Company who can work with you and help you better answer that question.
Take care and don't hesitate to contact us directly if you have any additional questions.
Annie and Bob Pacieznik "a name in real estate you might not be able to pronounce but can certainly trust" http://annieandbob.com