System clock out of sync on boot

[SeltiX]

After reporting this problem here : https://github.com/guysoft/OctoPi/issues/606 I was redirected because it should be a raspbian issue.

1 - Cut power off from raspberry pi ( without using the Shutdown system from UI )
2 - wait something like 5 or 10min
3 - Boot up raspberry pi
4 - Check octoprint.log, the timestamp will be equal or INFERIOR at timestamp before shutdown

I wold expect raspbian to wait for NTP sync but I already understood it may not be possible. I already understood too because raspberry pi has not hardware clock with battery is not possible to maintain the clock updated at start up, only after online sync with NTP server. But I wold expect to at least the time stamp wont be inferior to the one at shutdown.
For example at 2019-09-08 19:08:50,449 octoprint startup with a timestamp smaller than before shutdown.

https://github.com/guysoft/OctoPi/files/3589529/octoprint.log
https://github.com/guysoft/OctoPi/files/3589532/serial.log
https://github.com/guysoft/OctoPi/files/3589605/syslog.log

My system is a Pi 3B+ with OctoPrint 1.3.11 on OctoPi 0.16.0