This is not at all the behaviour I have found from setting these values. However, I have only really experienced them with the player. I would have to experiment, but I suppose it isn't impossible that the player is a special case.
A cut-down version if you wish to observe this would be;
onevent EVENT_GAME
ifactor APLAYER
{
setplayer[THISACTOR].xvel 102400 // Should be enough to make you move a little, but not fast enough to instantly smash into a wall.
}
endevent
I understand that the "ifactor" is redundant as I am using setplayer, but I use this "if" in my code because of other code that has to run exclusively in the APLAYER actor. I doubt it has any bearing at all, but it is included for consistency with what I have. Turning the player does not alter the direction in which they are traveling; A positive XVEL set this way serves to move the player towards positive X on the grid, regardless of which way they are facing.
This method is unusual for me anyway and is related to a specific purpose. Usually I just add/subtract X/Y/Z as I can safely assume the player won't be positioned outside of player space at any time the code is used.