affects 2.1.1, interface 'primary' ip changes to alias-ip when saving interface.
Affects pfSense 2.1.1-PRERELEASE (amd64) built on Sat Mar 8 (but also that of 20140219-1945)
I could not reproduce this behavior on pfSense 2.1 RELEASE.
logging in on the webinterface is not possible HTTP_REFERER check now complains when visiting the webgui using: 192.168.0.10 / anti lockout rule is also filtering on .20 , and in case the ip-alias was used for a different subnet it leaves you locked out of the webinterface.
install pfSense on a machine with one or more interfaces
-give WAN a static ip of: 192.168.0.10
-add a ip-alias on the wan with IP: 192.168.0.20
-go back to the WAN edit page, and save and apply the settings.
Running 'ifconfig' shows that 192.168.0.20 is the 'first' ip of the interface.