sweiser a question
From documentation (emphasis mine)
If you are using a Unix-like operating system, then you can set the system time zone by setting the TZ environment variable in your shell before starting the server. For example:
$ export TZ='America/New_York'
$ service mysql start
You are not using Unix-like operating system, why would you expect that to work?
I didn't expect anything, not even that this part of the documentation (which I did read in advance) is up-to-date, so I just tried it. And what I see is that it works in parts (MariaDB does apply the time zone, it just doesn't reflect it in the variable system_time_zone), so I assumed that it is a bug.
If I understand your comment correctly, the fact that is somewhat working right now is "an accident" and not intended. So maybe this should be better as a "task": "make TZ variable work properly on Windows too".
I would still point out that the current behavior is somewhat inconsistent, especially because the TZ variable might be deliberately or accidentally set to something even on Windows systems (for example, some old versions of Cygwin did set it during installation). That being said, if the solution to it being inconsistent would be to remove the current behavior entirely, that would make me sad. 