Do you have DHCP turned on for your router?
In the section located at mIRC Options - Connect - Local Info, do you have checks beside Local Host & IP Address in the area marked On connect, always get:
If not, try those suggestions and see what you get. Changing the DHCP settings will probably require a reset of your router. If this is necessary it should be done automatically.
I'm using a SMC Barricade 7004VBR with those settings and my IP address is returned correctly.
