Maybe another viewpoint will help. I use mm v 4.0. I tried the
example, no problem. I then tried:
foo = Graphics[{Blue, Rectangle[{1, 0}, {2, .1}], Red, Rectangle[{0,
0}, {1, .1}], Green, Rectangle[{0, 0}, {0, 1}]}]
Export["foo.pdf", foo]
Display["foo.tiff", foo, "TIFF"]
However I see the line in both the pdf and tiff: but not in the front-
end. And resizing does not reveal anything.
Checking the post-script code (alt-shift-e) in the front end Graphic
it's clear while there's "no width" on green, and changing the column
values will then shows green in the front end. However as I said
before, with an equal 1st column my pdf viewer decides to write a line
anyhow.