I can report the same- 12.04 install and on the "simple" firewall page, you cannot enter certain fields- e.g. forward incoming port 8005 to 192.168.80.5 port 8005.
I think you can get it done on the "advanced" firewall pages.
Quick edit to this- if you are on the "simple" firewall page and create a rule, if you click "edit" on the right hand side, you get to fill in more details (including the to: port). Still, the columns seem to be shifted over- for example, under "source port" you get a drop down box of the available protocols, not an option to enter the source port.
All I was trying to do was enable access on port 80 and 22. Clicking through "Outside Access" -> enable remote on 22 and 80 did not work. I can't be 100%, but I think clicking those boxes added rules to my firewall that don't make sense. For example, I now have 4 nearly identical rules that take source port "udp" and forward it to destination 67 (or 68 for two of the rules). "Allow DHCP" is written in the unnamed column to the right of "description".