The apparent lack of support for scheduling in UTC in much more mature calendar software (Google Calendar / Calendar.app) further suggests that this is not an important feature for most users.

In T11073#218937, @epriestley wrote:

Do you routinely schedule events in timezones other than UTC or your local time?

In T11073#218834, @epriestley wrote:

I'm just trying to understand whether this is a common problem that all users of Calendar software routinely experience

In T11816#218816, @epriestley wrote:

How do you currently schedule an event in UTC in other software?
I can't figure out how using Google Calendar -- I can't find any option in this dropdown which let me, but maybe I'm just overlooking it? There are approximately 9 million options. I looked for "International", "UTC", etc.

I have noticed some strange behaviour with recurring events, which I've first documented at Wikimedias Phabricator. It's about what every programmer I know hates: Daylight saving times. Short version is: Phabricator locks time windows of recurring events to the time the event creator had in his time zone settings when he created the event, but does neither give an option to select another time zone to lock to nor does even show which time zone this is currently locked to.