When you run a personnel action on the middle of the month, it will cause a split in the payroll period. Depending on the customizing of view V_530_E, field 'Account.split' (PERSP), it will generate a WPBP split or a payroll split at the moment of running payroll:
Period split for payroll accounting, possible entries:
Space --> do not separate payroll results
X --> separate payroll results
For Payroll Portugal, we, from the product team, suggest to read the KBA 2379613 - Scenarios where payroll split should be used to know when you should use a WPBP or payroll split depending on each situation.
In case the previous information did not solve your issue, please contact us (SCN, chat, incidence) providing the information described in the following link: How to report an incident to SAP Support about PY-PT.