I dowloaded your file and ran it on my XP system. For what it's worth, this does not happen on a windows XP system.
Thank you for your post.
I can replicate the issue on Mac OS X 10.5.8 and 10.6.3. I cannot replicate the problem on Windows XP.
This has been previously reported, and our Development and Software Quality Assurance (Testing) departments are aware of this issue. When more information becomes available, I will let you know.