PDF test file, OK in Acrobat, not in Illustrator?

I've posted to

 <http://www.stanford.edu/~siegman/illustrator_pdf_test_image.pdf>

a PDF test file (about 4 kB) of a test vector image which was created in 
Mathematic 6, displays just fine in Acrobat, but appears with grossly 
thickened lines if viewed in Illustrator CS 11.0.0 (all this on a 
MacBook under OS 10.4.11).

If anyone has the time and skills to open this short PDF file and give 
an opinion as to whether there is anything odd about its PDF coding that 
might cause this problem, or whether it must just be a bug in 
Illustrator 11, I'd welcome the information.

Email replies also welcomed.

[Note: This is a follow-on to a similar posting I made earlier with a 
different test figure, for which some respondents encountered the same 
behavior in Illustrator 11, while others found no trouble when it was 
opened in Illustrator 12 or 13, or versions prior to 11.]