Vanishing vector fills... I'm stumped. HELP!

Question

When creating PDF documents from any software (Illustrator, Corel, InDesign, etc), vector objects with a fill other than white, that are over 50% of the page size, have white fill in Acrobat 9 Professional.  If object has an outline, the outline will appear normally, but the fill will be white.
I've searched to the furthest reaches of the internet and found no answer. Most forum topics on similar issues focus on the program that exported the PDF. I am 100% sure this is not an export problem, but is something in Acrobat itself (a missed setting? Corrupt program file?)  
To provide the best information, I've done a little scientific research. Here is what I know:
Working in WIndows Vista 64bit
Currently running Acrobat Pro 9.5.5
This is only happening on ONE install of Acrobat 9. Documents display correctly in Reader X and in Acrobat 9 on other machines.
Started happening a few months ago.
"Show Large Images" in preferences dialog is checked. Unchecking it and rechecking it does nothing. This is the most common "solution" offered on internet forums.
Have installed all available updates to the software
I experimented with different object sizes. At 50% of page size, vector objects appear normal, at 51% vector object fills disappear.
Does not affect bitmap images, only affects vector objects.
Things I've tried to solve this:
repair the install.
uninstall and reinstall
check "show large images" in preferences... over and over
cuss at the computer
throw a tantrum.
I welcome all ideas to fix this.

Answer 1

I've tried several ways, several settings, and from different programs until I realized the problem isn't with the file.
I generally work from CorelDraw X5 and export to PDF. But that isn't the issue in the least, as I stated above. I am 100% sure that it has nothing to do with export or what program I am using to export... here's why:
PDFs look fine on other computers with the same version of Acrobat. They look fine in Reader. They problem is only in one install of Acrobat. I've identified that the problem happens when a colored vector image takes up more than 50% of the page space. Under 50% it appears fine, over 50% the fill becomes white (not transparent, but white).