I just imported an event ics that went over midnight. The import went OK, the event shows up in overviews, but in the calendar the event is not displayed.
Seems to be because events that are over midnight can't be set. This is of course not good in itself, but until that is fixed/possible maybe the import could complete with an error or a hint that the event will not be visible until its end is set before midnight or the import could simply set the end to 23:59 and show a message that it did?
But in any case: PLEEEEEAAASE make events over midnight possible as soon as possible!