Logout times for users are correct if user logs off and then shutdown from gdm, however logout times are wrong if user shutdowns directly from the user session, because boot time is used in this case.
wtmp contains also shutdown records. Logout time should be set to the time from shutdown record instead.
One can list those records using "last -x", it looks like as following:
shutdown system down 4.4.3-300.fc23.x Mon Mar 7 08:13 - 08:14 (00:00)
See last source codes:
See original g-c-c report:
Created attachment 124758 [details] [review]
wtmp: Fix logout times in login-history
Set logout time to the time from shutdown/reboot records instead of time from BOOT_TIME record.
Created attachment 124759 [details]
users panel screenshots