Adobe Illustrator PDF displays incorrectly in Apple's Preview application
I tried to export my AI file from Illustrator (Save As..) as a PDF, but for some reason, the logo come out very badly.
The exported file ends ups like this : http://d.pr/i/SySs
( I looked at the pdf on dropbox, and it looks fine. But for some strange reasons, in Preview it looks like the image above. It's pretty strange. )
Apple's Preview application has horrendous issues with some items - spot colors, transparency, overprints, etc. If you see strange behavior in Preview, the first thing you should do is check the PDF in Acrobat or Reader.
That triangle is constructed of several objects all using transparency (Blending modes). Flatten the transparency and it should look as expected in Preview.
If you need to correct the display of a PDF in Preview you have to "dummy down" the objects. Convert spot colors to RGB if possible, flatten transparency, remove overprints, etc.
It's an Apple issue, not a PDF (or Illustrator) issue.