i don’t see a bug here. unless anything changes, i believe that when you upload via the website,
since you changed the time zone in your account settings between the 2 uploads, you got two different time zones applied to your observations. it’s definitely a quirk, but i think this is technically how the system was designed to work.
i think the best course of action in this case is just to fix the times whichever observations reflect an incorrect time.
it may also be worth noting that there’s a feature in the upload page that will allow you to offset times. not sure if that helps in this case, but it might help in future uploads.