EDIT: I've tried playing LoZ II on my toaster box style NES and have the game lag/status bar corruption issue, so I guess it could be said that the Retro Duo IS able the play the game exactly the same as an original system.
However, I have not tested it on one of the newer top loader NES systems to see if occurs there. (I need to get one and then mod it for A/V support.) I still need to take a photo of the difference in color palette for the sand on the overhead map though.
Just to clarify though, my copy is the original Gold Case release. Is your copy the same or the re-released gray case? It could be a version issue that was later corrected.
Also, Castlevania II: Simon's Quest does not have correct music channel support with the Retro Duo. All I hear when playing the game on my Retro Duo is the bass effects. I tested it on my original NES Unit, a FC Twin and the FC Dual and on those systems I hear all the music channels, so it is not a problem with my cartridge. No other games have this issue with my RD, so it seems safe to assume it is a hardware limitation for that game. Possibly caused by whatever hack/mod was required to get CV III to work?
can you show pics or a video of what you mean? my game plays perfectly fine...