Noticed another one: landing after doing a running jump pushes me backward a bit instead of smoothly continuing forward movement. It happens every time I land, but is more noticeable after longer falls.
Viewing post in small graphical inconsistency (almost fixed)
I will need to look into this. I don't remember if the movement code is so old it uses Game Maker's built-in collision system, if that's the case it might explain what's happening (colliding with a solid object cancels the ongoing movement and requires you to manually reapply it if you wanted to get as close as possible - like sticking to the ground when landing).