I could understand why this glitch would've gone unreported for all this time, because why would anyone in their right mind play the US version of Castlevania III on an Everdrive N8 when you can play the vastly superior Akumajou Densetsu?
It's not necessarily better, just different. There are some tweaks to the US version that make it more of a challenge. Nerfing Grant (or buffing, depending on your point of view). Different damage scaling. Faster projectiles from enemies. A tougher final battle. It all depends on what you're looking for.
Really, though, is this an issue with the MMC5 implementation that's been there from the beginning, or is this a recent occurrence? I wish that chip were supported a bit better beyond just getting
Castlevania III functional. (And yes, I know a lot of the Koei games have issues related to limited PRG/CHR space.