Why does the range type's upper function behave inconsistently?

I don't understand the inconsistent behavior of the range types' upper function in regard to inclusive ranges.

For example(s):

1. SELECT upper(int4range(1, 4, '[]')) = 4; -- FALSE
2. SELECT upper(int8range(1, 4, '[]')) = 4; -- FALSE

3. SELECT upper(numrange(1, 4, '[]')) = 4; -- TRUE

4. SELECT upper(tstzrange('2015-07-01: 00:00:00', now(), '[]')) = now(); -- TRUE

5. SELECT upper(daterange('2015-01-01', current_date, '[]')) = current_date; -- FALSE

#1 & #2 are FALSE because upper returns 5 instead of 4; and #5 is FALSE because upper returns: current_date + interval '1 day'. I don't understand the logic behind why it would return the inclusive upper bound value for some ranges and not others. If anyone can shed some light on this behavior it would be greatly appreciated.

One of things I originally tried to use upper for was CHECK constraints. That was until I wrote some unit tests and realized that upper doesn't consistently work the way I expected. Of course my assumptions are probably wrong so that's why I'm asking for clarification.

Regards,