USB key fails to authenticate at GUI login screen

[zz0rk]

I am running pam_usb 0.5.0-4 on Jessie 8.5 with Mate Desktop. When I try to log into my workstation at the login screen I experience the following:

a) when the profile is set to 'sufficient' the USB key fails to authenticate automatically and the workstation remains locked; I have to use my name and password to log in.
b) when the profile is set to 'required' with the USB key connected and using my name and password authentication fails; the password is wrong.

At the CLI everything works for either profile setting (sufficient or restricted).

Update Fri Aug 5 06:43:26 PDT Fri Aug 5 06:45:13 PDT 2016:
1st time login at boot works as expected; it's subsequent logins after the screensaver kicks in that fail as described above.

[zz0rk]

Debug output. Authentication with key only fails once the screensaver has been engaged. First time login after boot works!
If someone could help me with this, I would really appreciate it.
Thanks

At screensaver:
Aug 10 09:22:42 myLaptop pam_usb[24661]: pam_usb v0.5.0
Aug 10 09:22:42 myLaptop pam_usb[24661]: Authentication request for user "USER" (mate-screensaver)
Aug 10 09:22:42 myLaptop pam_usb[24661]: Device "derKey" is connected (good).
Aug 10 09:22:42 myLaptop pam_usb[24661]: Performing one time pad verification...
Aug 10 09:22:42 myLaptop pam_usb[24661]: Pad checking failed !
Aug 10 09:22:42 myLaptop pam_usb[24661]: Access denied.
Aug 10 09:22:51 myLaptop mate-screensaver-dialog[24661]: gkr-pam: unlocked login keyring

At CLI:
Aug 10 09:23:34 myLaptop pam_usb[24736]: pam_usb v0.5.0
Aug 10 09:23:34 myLaptop pam_usb[24736]: Authentication request for user "USER" (login)
Aug 10 09:23:34 myLaptop pam_usb[24736]: Device "derKey" is connected (good).
Aug 10 09:23:34 myLaptop pam_usb[24736]: Performing one time pad verification...
Aug 10 09:23:34 myLaptop pam_usb[24736]: Access granted.