if your UK employer pays you from an Irish paypoint then it has to apply the Irish PAYE system.
Also if your activities mean that your UK employer has a branch in Ireland, then Irish PAYE should also be applied.
If you are paid directly from a UK bank account and the UK company does not have a branch in Ireland, then Irish PAYE may not apply. In that case your income is probably taxable as Schedule D Case III income rather that Schedule E (PAYE) income.
If your employer is operating Irish PRSI it sounds as though they have probably obtained tax advice on this matter so you should go to them with any concerns you have