While I can’t comment on Pennsylvania law in particular, in general a patient cannot be billed or be required to pay medical invoices while a Medicaid application or an administrative appeal is pending. If the patient loses the administrative appeal and then goes on to appeal to court, they will be liable for paying the bill. Of course, most Medicaid applicants do not have the necessary funds in any case.
To get a definite answer, however, you will need to consult with Pennsylvania counsel.
Read more about Medicaid's rules.