Whenever I stroke a path with rounded corners on iPhone, the rounded corners are thicker than the rest of the stroked path. See here for what I mean:
rounded corner thickness http://img181.imageshack.us/img181/6372/screenshot20100320at123.png
Not sure why this happens, any ideas?
I agree with Peter Hosey's analysis that the outer half of your lines is getting clipped off, but my recommendation would be to move all the coordinates .5 pixels inward instead. This way your straight lines will be crisper (not antialiased across 2 screen pixels) as well.
