Well... I'm getting a glitched screen with a few games, noticeable in MMC3 games like Rad Racer 2 and Gauntlet 2. The same thing appears in the cooper bars demo: glitched "pieces" of lines at right. Links to screenshots below.
I (obviously) use the loopy's ppu logic, and doing the 2007 I/O with this same 15-bit address, rendering the screen by reading it directly. Is there any special thing regarding the scanline rendering?