After digging through the movement code, I think that some of the "weirdness" in object movement (most of the times it behaves OK, but sometimes it is really strange) comes from the fact that objects move horizontally first. So, if an object has xdir 100 and ydir 100, it will try to move 10 pixels to the right first, stopping if there are any collisions, and only then it goes down. Looking at this I am surprised that diagonal movement (jumping, thrown objects) work well in our game :D, but of course the velocities from jumping and throwing are usually so low that the effect may not be as noticeable.
After the pull request I *might* want to try a branch that has a different motion strategy, with the following conditions:
* it is really just experimental, so I will not be surprised if we decide to not change that
* it may change the behavior of objects significantly, maybe breaking existing "veteran tricks" or even existing scenarios that rely on the current behavior
* it needs a good testing scenario that contains some typical movement patterns from the game, as well as the special cases here. This can and should be done before creating the branch, though :)

What are your opinions?

Edit: Moving horizontally first may have something to do with the gravity movement, just a note for myself.