Oh my, I am in Lakeport!!
According to CAMFT Attorneys (link below), in CA we are not required to return insurance over payments unless requested to do so. Also, there is a statute that says "reimbursement for over payment...shall not be made...unless written request...is sent".
With that said, if I get a duplicate payment or incorrect payment from Medicare, that is obvious, I return it. With Partnership HP, they probably would not know what to do with it if you sent it back without a request for return. Many times, I find that the system over adjusted leaving a credit, so check that as well.
The best way to know for sure is to contact the payer. Sure enough, as soon as you send money back unsolicited, the other payer comes at you with a demand for return of over payment. You could keep the credit reflected in the account with a note of why it's there so that when the demand arrives, you have all the details, but hold the credit until a demand for return is received. Just something to consider...