It's possible it's caused by slight differences between the Japanese 9929 and the American 9918, another possibility is that CRT scanline gaps might give the illusion of serrated edges.

*edit* Just to be sure, you might want to inform blargg about it, so he can look into it. His email address is at his homepage.

Come on... trust me... I can see the difference of serrated edges and CRT scanlines

BTW as Japanese PX-7 is 60Hz machine the video chip must be TMS-9928/A (I just looked the video chip from MSX-FAQ)

Although I've seen tons of different european MSX-machines the PX-7 is only Japanese MSX-computer that I've seen connected to Japanese monitor with composite. With european MSX's I have not seen anything like this to happen. IIRC this artifact does not happen in PX-7 if you connect trough RGB, but I'm not sure about this. How ever I'm sure that I've seen this artifact as it really amazed me first time as I had not ever seen anything like that before.

Maybe some Japanese reader could comment this issue?