Date time like DTSTART:20191113T120000 are considered like floating date time in RFC5545. This commit modifies the readICalDateTime function not to use the system time zone in that case, but the LocalTime spec. Otherwise, there is no way to distinguish incoming floating time from time given in the system time zone. Then when exporting to iCal format, the floating format is not conserved.
Also properly export date time in UTC using the Z character and not TZID=UTC as mentioned in RFC5545 section 3.3.5: "The "TZID" property parameter MUST NOT be applied to DATE-TIME properties whose time values are specified in UTC."
This one is also a MR I forgot about during the phabricator migration, see https://phabricator.kde.org/D25289
There were some discussions on-going there that may be of interest to read when reviewing again this proposition.
Thank you !