Why does the time setting in win affect ubuntu and vice versa?

Question

System administration

On the same machine, windows 8.1 and ubuntu are installed on different disks.
When I set the correct time on one of them, it shifts to the other by several hours.
When you reboot, the time in the system is not reset, only if you change it in another system.
In the BIOS, the time is correct, the time zone is also set correctly in both systems.

Answer 1

It seemed that this was some kind of complex and unique problem, so I didn’t guess to look in the most obvious place:
help.ubuntu.ru/wiki/%D1%81%D0%B8%D1%81%D1%82%D0%B5. ..