ical-recurrence: test that an ExceptionDateTimes in another time zone excludes removeExceptionDatetimes compares DateTime values structurally, so it only ever excludes an instance when the constructor and the time zone identifier match exactly. RFC 5545 constrains the value type of EXDATE to that of DTSTART, but not the time zone it is given in, so the calendar in this test conforms and its EXDATE names the second instance unambiguously. It is silently ignored. Matching should happen on resolved instants instead.