FWIW - I have Marco's PPA package installed and I continue to see this issue.  Another issue that seems partly relevant is that my screensaver never stays on for more than a few minutes before I see the lock screen again.  I notice that when this happens, this issue is more prevelant.  Here is a snippet of my auth.log (note that I, nor anyone else is at the office during this time frame) and 6:25 is when I first sat down at my desk to log in.

    212 Dec  2 04:40:14 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    213 Dec  2 04:52:04 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    214 Dec  2 04:52:04 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    215 Dec  2 05:03:52 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    216 Dec  2 05:03:52 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    217 Dec  2 05:15:42 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    218 Dec  2 05:15:42 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    219 Dec  2 05:27:30 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    220 Dec  2 05:27:30 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    221 Dec  2 05:39:18 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    222 Dec  2 05:39:18 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    223 Dec  2 05:51:06 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    224 Dec  2 05:51:06 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    225 Dec  2 06:02:55 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    226 Dec  2 06:02:55 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    227 Dec  2 06:14:43 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    228 Dec  2 06:14:43 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    229 Dec  2 06:25:41 d000-mzuba1 unix_chkpwd[14694]: check pass; user unknown
    230 Dec  2 06:25:41 d000-mzuba1 unix_chkpwd[14694]: password check failed for user (mzuba)
    231 Dec  2 06:25:41 d000-mzuba1 compiz: pam_unix(lightdm:auth): authentication failure; logname= uid=1002442509 euid=1002442509 tty= ruser= rhost=  user=mzuba
    232 Dec  2 06:25:41 d000-mzuba1 compiz: gkr-pam: unlocked login keyring
    233 Dec  2 06:25:41 d000-mzuba1 unix_chkpwd[14703]: could not obtain user info (mzuba)
    234 Dec  2 06:25:48 d000-mzuba1 compiz: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
    235 Dec  2 06:25:48 d000-mzuba1 compiz: PAM adding faulty module: pam_kwallet.so
    236 Dec  2 06:25:48 d000-mzuba1 compiz: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "mzuba"
    237 Dec  2 06:25:52 d000-mzuba1 unix_chkpwd[15012]: check pass; user unknown
    238 Dec  2 06:25:52 d000-mzuba1 unix_chkpwd[15012]: password check failed for user (mzuba)
    239 Dec  2 06:25:52 d000-mzuba1 compiz: pam_unix(lightdm:auth): authentication failure; logname= uid=1002442509 euid=1002442509 tty= ruser= rhost=  user=mzuba
    240 Dec  2 06:25:52 d000-mzuba1 compiz: gkr-pam: unlocked login keyring
    241 Dec  2 06:25:52 d000-mzuba1 unix_chkpwd[15015]: could not obtain user info (mzuba)