I recently upgraded to Adobe Reader 9.1.1 on my IMAC with a recent upgrade to Leopard 10.5.7.
Since then, I've noticed a lot of extra, thick horizontal lines appearing when displaying a document and scrolling down the page, but the lines disappear when I scroll up or move my mouse focus off the document and back to the dektop.
Someone suggested this is a result of corruption in the fonts or font caches. I deleted all caches that utility programs will allow me to delete, including the font cache, but the problem persists.
I called Apple tech support about it, but they just passed the buck to Adobe.
I was unable to capture this problem with a screen dump.
I suspect it is an Apple OS problem, not an Adobe problem.