Strange behaviour with personal events

I observed strange behaviour when creating personal events:

• Once, creating a personal event failed with an Internal Server Error (I could not reproduce to get a stack trace later), but after a reload, the event was there
• I changed the date of the event – it vanished from the calendar view, but did not appear on the new date. After a reload, the event was visible on the new date.

added type::bug label

added core-4.0 label

assigned to @yuha

assigned to @ZugBahnHof and unassigned @yuha

assigned to @yuha and unassigned @ZugBahnHof

created branch 1162-strange-behaviour-with-personal-events to address this issue

mentioned in merge request !1733

may be connected to #1221

to be exact, it seems that as a non-admin user, you can't create personal events at all