Could you share an example of what is going on, i can not seem to get my head around what is going on.
But there is no way of animating 8 directional movement without changing the core game. also 8 directional movement is not true 8 dir in the normal sense, but let me diverge a bit first.
The map is a grid with squares, your character moves one tile at the time until you hit a non movable tile. if you wanted true 8 directional movement you would need to Octogons
As you can see this would give a true 8 directional movement, but the sprite used for RPG maker has only 4 directions, like this.
The game is also programmed to read the sprite with 4 directions and i have not seen anywhere a way to easily change this without rewriting the entire code (this is possible, it is not difficult, but might take a while)
to fake diagonal movement what you do is divide every title in smaller squares and move within those.
I am far from an expert on this, sprite and graphic drawing is not my forte, but this is my hones opinion, but i could also be wrong when i say; I do not think drawing a 8 dir sprite would actually work right out of the box.
Could you at lease provide me with a link to your movement plugin and i could be sure of what i say is correct? ;)