I dont know how much people have actually examined the occurrence of that bug to be honest.
it was discovered quite early in nesmaker's life when most people around here including myself had no slightlest clue about how assembly or the game engine worked at all, and the whole thing was just kinda accepted as a thing
that doesnt work and forgotten heh (not too many people tried to make that big of monsters anyway.)
I honestly cant say if im even remotely in the right track with the whole thing, especially since my own research into the matter has been minimal at best. but that's pretty much where i will eventually start looking for,
when im gonna get it fixed (assuming i ever need to.)
I could post you a full metasprite draw routine if you're willing to deal with writing object tables by hand, just be warned that using mine comes with a wide array of drawbacks such as no hitboxes, no collision detection, and now readily controllable
object parameters, meaning every single thing you wish to do with the objects has to be punched in by hand.
As an added bonus, my metaspritedraw draws directly into VRAM instead of going through nesmaker's objecthandler or sprite draw, meaning that it is completely void of things such as flickering or whatever else you may have there.
doing one's own metasprite system is a wide range of work heh. Personally, i just use it for weapons but even so, generating few frames of animation and a static hitbox for those alone was a week of scratching head and punching in sprite offset tables.
i dont even want to know how much work it would be to adapt it for making an actual monster that moves.