I am facing this issue in Ical.Net Version=4.0.1.0 and lower, When we get "GMT-0500" in DTSTART/DTEND then it is giving same utc time as local time in AsUtc. But If I replace "GMT-0500" to "Canada/Eastern" manually in ics its giving correct utc time in AsUtc.
Following is not working fine -:
DTSTART;TZID=GMT-0500:20181213T190000
DTEND;TZID=GMT-0500:20181213T220000
Following works fine -:
DTSTART;TZID=Canada/Eastern:20181213T190000
DTEND;TZID=Canada/Eastern:20181213T220000