Tax Basis F1, am I being over taxed?

[paynie]

My tax code is normal "A", as is my PRSI "A1". But my Tax Basis has changed from "0" to "F1", I seem to be paying more tax than I did before.

Can anybody help and tell me what this F1 means, I've looked on the revinue site but have found nothing.

Thanks in advance paynie