Comment 29 for bug 737615

The problem is unexpected order of user input resulting in "unsavable" data.
Input fields MUST be finished with an ENTER keypress or the data validation is apparently incomplete.
Sadly, the colored red to green background validation misleads the users into thinking the entry for each of the three fields, Address, Netmask, and Gateway is complete.

Problem could be mitigated by adding to hover help text.
Problem could be solved with data validation when click the "Add" button alongside "Addresses".
Or creating a flag for each of the three fields, all of which must be set to valid, for the Add to add a new address. A popup or some other indication, say blinking or turning all invalid fields red, could then direct the user to fix the bad field data.

Reproduce by:
Editing a connection
Select the "IPv4 Settings" tab.
Change the Method pull down to "Manual".
Delete any existing addresses.
Click Add
Type 192.168.1.49 (entry will turn from red to green)
press TAB (not Enter)
Type 255.255.255.0 (entry will turn from red to green)
press TAB (not Enter)
Type 192.168.1.1 (entry will turn green)
Press Add
Save will be greyed out but entry will appear as a row within addresses.

Also reproducible by clicking into each field rather than pressing TAB.

Workaround. Press ENTER after EACH entry rather then pressing TAB or clicking to the next entry.

Easy mitigation: Change hover text from:
IP addresses identify your computer on the network. Click the "Add" button to add an IP address.

to

IP addresses identify your computer on the network. Click the "Add" button to add an IP address.
Then enter Address, Netmask, and Gateway, pressing the Enter key after EACH entry.

This is perhaps icky, but might save others sanity :-)

Note: when you TAB from 199.168.1.49 to "Netmask" the number "24" appears automatically in the field.
Perhaps this is an indicator of the 24 bits that compose an old "Class C" address.
Pressing Enter after the 24 is displayed (and after click or TABbing to Address and press Enter, and after clicking and TABbing to Gateway and pressing Enter) allows you to save the Address. When you return to the re-edit the address the 24 has been automagically converted into 255.255.255.0.
No indication of this lovely and useful magic is on screen or in hover help text.

Thanks to for the clue to the problem:
> jlinkels (jlinkels) wrote on 2011-05-21: #6
>Well, you can make the save button ungray, but you have to press ENTER after entering the IP address, >the netmask, etc.