Hi Fredg,
I was the same problem, in my case that works only if I use the default admin user, with another administrator account create by the menu user manager, it doesn't work.
( my configuration Alix 3 lan interfaces, m0n0wall 1.3 )
Ding ding ding....BINGO. Thanks pat2003.
I can conform this behavior. Logging in with username: admin and Secondary IPs can be configured. Logging in as another user and Secondary IPs cannot be configured.
I believe this is a genuine bug.
Unable to confirm here unfortunately. The secondary IP screen works with the default admin account as others have said, I then created another username (clear out all the firefox cache and preferences, restart firefox browser), login as that new username, go to the same section and the Secondary IP screen still comes up as it should, no redirection to the wrong place or anything.
Running 1.3-Release Generic PC image
I've attached a screenshot to show, you know it's a user account because on the left side is the "user password" screen for users to set their password.