Eircom are currently several firmware versions behind ZyXel for the F1000. The current beta release from ZyXel UK includes a fix for port forwarding bugs, in particular where a resync takes out the applied rules.
For those who are interested, and understand the risk that you may kill your F1000, I attach a full log of an F1000 unlock followed by flashing both the ZyXel bootloader and the latest firmware. Commands are in blue, comments in red in the PDF.
You will need a phillips screwdriver, a USB-TTL serial cable, communications software that supports serial and xModem protocols, but no soldering skills as the board comes with a serial header.
I do not encourage anyone to do this, I simply pass on the know how to those who wish to do it. You know who you are
NB: Do NOT use the Vcc connector on the header. Serial is 115200baud, 8bits, no parity.