GNOME Bugzilla – Bug 731637
Screen saver causes user list to use focus, have to use mouse to select user
Last modified: 2014-07-14 21:27:57 UTC
If the screensaver is activated while gdm is running, after closing the screensaver the user list does not have focus and the tab key can't be used to focus it. The mouse has to be used to select the user. This is very annoying for people who like to avoid mouse use as much as possible (eg. to avoid RSI or just to do things more quickly). https://ask.fedoraproject.org/en/question/34305/gnome-3-gdm-login-using-keyboard-only/ has a good description of this problem.
Although this bug report is pretty old now (and it seems to have 4 duplicates, #701518, #733014, #712541 and #708105), there *is* a solution, although not documented. You may press Ctrl-Alt-Tab to cycle between login screen elements, including the top bar. This, however, is only a workaround, I hope someone fixes this issue soon.
Thanks for the bug report. This particular bug has already been reported into our bug tracking system, but please feel free to report any further bugs you find. *** This bug has been marked as a duplicate of bug 708105 ***