Welcome to the ZDoom Forums!

There isn't much that can be done about it. The checks that are performed here are too crude to address every single edge case. The real problem, though, is that every time something like this is attempted to get fixed, other more serious issues will spring up.

That's why I won't touch it and also recommend to others not to touch it.

This is probably the same behavior that causes items to "jump" to the top of moving lifts, if the hitbox for the item overlaps the moving sector.

There's something unusual happening when using a chainsaw in an opened doorway.

If:
1) I'm using a chainsaw against a demon in an opened door sector
2) I'm walking or pushing towards the same demon
3) the demon dies and at the same time the door attempts to close and bounces back

The demon in it's death sequence might jump on top of the player. I've noticed this happening in door sectors only when the door is moving.
[spoiler][img]http://i.imgur.com/u3YVu4N.jpg[/img][/spoiler]
Here's a test map to try this (Doom2; MAP01). It includes a demo lump recorded with zdoom-2.9pre-928-g841a579 but it plays well even with zdoom-2.9pre-415-g346fae8.
Run the pk3 with ZDoom, start a new game and type into the console: 'chase 1' and 'playdemo chainsaw.lmp'. It's easier to see from the chase cam view.