ah good. i was just about to report that bug. it doesn't seem limited to diagnal ones though.
i first had the prob on arena, and i thought it got fixed at some point, but i just noticed it on newbie tonight. only two checkpoints, but appear straight, and you need to run over the flags.
heh, i diden't even know they could be diagonal either.
and the diagonal checkpoints i found to not work i only found because i was about to redraw them where they already were, and found that the one flag was on an adjacent tile to the line from the first flag.