barlines print out at inconsistent widths with Preview (Mac OS X 10.6.x)

[Arle Lommel]

I've noticed occasionally in the past, and now once again with 2.13.29, that 
Lilypond-generated PDFs often print out with variable width barlines (even 
though the PDFs appear fine at all magnifications) when printing from the 
Preview application on Mac OS X 10.6. The problem does not seem to occur when 
printing from Adobe Acrobat Professional 9, so this is almost certainly a 
problem with non-Lilypond software, at least in part, but I'm wondering what 
about Lilypond-generated PDFs might be triggering it.

I have attached a scanned image of a printout from Preview of one score that 
shows the problem, with a blow up of the scan showing the individual pixels for 
one area where the problem appears. As you can see, it's a pretty striking 
difference, with the heavier barlines about 50% thicker than the thinner ones:

For what it's worth, I'm printing to an HP LaserJet 1300 (I don't have another 
printer handy to test this on right now) and am printing from. I opened the 
file in Illustrator and the barlines of different thicknesses seem to be 
identical in the PDF (.93 pt), but as you can see from the scan there seems to 
be no rhyme nor reason to this. It wouldn't seem to have anything to do with 
image resolution since these are all vector graphics, so does anyone have any 
idea what might be going on or how to fix it.

The obvious work-around is to print using Acrobat, which I will do, but it’s 
still a curious problem. Any thoughts?

Best,

Arle