Just asking if any one has seen this error before?

For me, during weekday I use my work machine to log in to Stack Overflow and during the weekend, I use my own laptop to log in.

I'm pretty sure that I did log in to Stack Overflow over the last weekend but when I go to work today and log in to SO with my work machine, it shows a record that I didn't log in to SO on the last Saturday and Sunday!

I have no problem with that, just want to report the system's error if it really exists!