I wanted to make a level with more than one midway points.
But you can't set in the editor more than one 'Midway entrances'.
So what I did... I edited World 1-1, and set a new Midway Point in Area 2.
But... sadly, it didn't work. If Mario came through the second Midway Point, you didn't see appear the flag.

But after that, I let Mario kill himself, and start again World 1-1.
Something really strange happened... It did work! At least, Mario begon at the place of the second Midway Point!
But at the bottom screen, there was still one flag, and it was on the place of the first Midway Point.

My question: HOW CAN THIS? WHAT'S GOING ON?
Here's a Patch with a edited World 1-1. (First Midway Point moved to beginning of the level.)

Well the original game never used 2 midway points (or did it..?) so it doesn't load that kind of stuff right.

Yes, I know that, but I'm wondering why it however works? Well... it works sort of...

The game keeps track of a single boolean value (true / false) to know whether you have the midway point or not.

So these glitches are to be expected. It can't remember which midway point you have gotten.

But I think it also keeps which area the midway point is in. Every area has the entrance id of the midway point, but a level doesn't know which area the midway point is in.

That might explain why you did get it working with two areas.

Not sure, though.