The custodian is responsible for paying the funds held under the PA UTMA to the minor or to use them for the minor's benefit. On its face, a transfer from the UTMA account to the custodian's personal account would seem suspect. However, it's the use to which the funds are put that is important.
The bank is not responsible for monitoring the transactions made in the account. However, if the bank learns that the use to which funds are put after leaving the account is not in agreement with the "pay to or use for minor" requirement, it could have a responsibility to report the activity under FinCEN's SAR filing requirements (assuming the dollar amount is large enough). If the UTMA remains open, the bank might consider closing it, remitting the balance to the custodian with a cashier's check on which the payee reflects exactly the ownership of the account, i.e., in the form "John Smith, Custodian for Minor Jones, PA-UTMA."