Two issues.
- When looking for timezone differences (regardless of the current winter/summer time), the
calc widget will select the summertime variant of that timezone - yielding the wrong answer.
- Despite the widget selecting the current timezone (e.g. AEDT) by default, using the summertime variant as part of the query results in
unknown.
Here, I test two timezones. EET/EEST and AEST/AEDT (AEDT being the summertime). Currently it's EEST in East Europe while AEST (winter) in Eastern Australia.

I'm unsure how the EET/EEST is parsed, but AEST seems to be parsed as AEDT (note the output)
EET to AEST is UTC+2 to UTC+10, so there should be an 8 hour difference. Yet, the AEST is parsed as AEDT, while AEDT as query results in error. Meanwhile, EET and EEST are not parsed properly at all, as 11.30 AM EET to AEST should yield 7.30 PM AEST; and 11.30 AM EEST to AEST should yield 6.30 PM AEST.
I would expect the timezones to be parsed as they are, regardless of the current timezone. That is, if I ask for the difference between EEST and AEST, that should yield a different response to when I ask for the difference between EEST and AEDT (because yes, this does happen a few days in the year).