An event over days: last day wrong

Well, first post here: timely people. Good, great even, but:

I do have an issue with the calendar, which is:

An event, starts at 10:00am on Friday 09 December to Sunday 16:00pm on 11 December

I work this as repeating and it closes on Sunday, last day, at 14:00 pm, not Monday.

So my question is this:

Is it North American to say “until Monday” and that means closes on Sunday. If that is the case, we have two different semantic views on the understanding of this statement.

Or is it a bug?

I have to make a bullet point on the event: closes on Sunday. Because people will be turning up, on Monday. This is not trivial, but really important.

If it is a bug, needs to be fixed.

Or I have to look to alternatives.

I know this has been going on as an issue, but it is a show-stopper for me. Can’t get dates right.

This will be a complete good bye for me, unless I can see a way, that doesn’t involve having to say “disregard, stops on . . .”

Think this is very important, to your very core.

Martin