I'm attaching an .mfa with two frames that should do the same thing: move the two cubes together 20 pixels up per frame if the top box is located directly above the bottom one (or if it overlaps).

The slightly more complicated version in frame 1 that involves moving around the objects more does not work. This causes a lot of problems when dealing with complicated custom movements involving objects that interact with each other (e.g. moving platforms that needs to move another object to check if it's own move is possible, or blocked by the other object).

Switch events 8 and 10 under the green block like this: [attached] is that what you need?

Sorry, I'm not in need of a workaround (I know those already), this is a bug report. If I needed programming help I would have asked. My events are correct, and I'm not getting the desired results.

Your solution have no relevance in the actual games I develop where this causes a problem, those cases are much more sophisticated and I can't move around events randomly like that. I'm not trying to repair a broken MMF2 elevator here, I'm just reporting a bug using the simplest possible example I could create that demonstrates it.

This is not a bug, this is the way the program works.
When you do an overlapping condition, only the coordinates of the first object are the most recent ones. The coordinates of the second object must be updated by a screen refresh to be taken into acount at their new position.
So in your first frame, you change the coordinate of the first object twenty times, but the coordinates of the second object in the overlapping condition never change, except from one frame to another. This is why your objects only move at 50 fps.
I do not think there is a way we can modify this, so you will have to find a way around it, like you have done in the second frame.

Ouch! Okey, I'll keep that in mind then when I design custom movements, object interaction is going to get so much messier than I had hoped for though...

Oh you edited your post out, hah. I saw it in time!

I had to change it, realized I had misunderstood Francois...