After logging into Stack Overflow for the first time in a day, I usually go straight to my Stack Exchange network profile to look for any changes across my 11 accounts.
I've noticed that although I've only visited Stack Overflow, each site displays "last seen today":
If I go into each site individually, (apart from SO which I have visited), they correctly report "Seen: X hours ago", e.g.:
I'm in the UK so my time zone is at most 1 hour different to SO's UTC day.
I'm wondering if this is a bug or if there's some logic/reason behind it (the explanation would be welcome).