I've restarted work on my Matchie game after finding a solution for an annoying TIA quirk. Although the 2600 shows 160 pixels across the screen, SCORE mode can corrupt the color of the last HALF-pixel on the left half of the screen. If the last playfield pixel on the left half of the screen is set, the 77th through 80th pixels should appear in P0 color. Unfortunately, the right half of that playfield pixel will show up in an indeterminate color which may be affected by COLUPF even though the playfield should appear entirely in P0 and P1 colors.
For quite awhile i shelved the game because I couldn't get it to look good on a real 2600. Finally, though, I figured out the solution: display Missile 0 at pixel 79 on any scan line where that playfield pixel is set. Problem solved.
I'm curious, though, does anyone know any other race conditions that can cause Atari 2600 to be "split"?