IE Mac was discontinued more than two years ago, and it just doesn't handle CSS Positioning very well.
If this is a really big issue for you, there might be some things we can do (but we'll stop short of making the code invalid), but the general advice would be that Macs using IE need to migrate to a newer browser, such as Safari or Firefox.
The following is a note that we sometimes display on complex pages after a browser detect for IE/Mac:
You are using Internet Explorer on Macintosh.
Due to a lack of full support in IE for modern internet standards (CSS-Positioning support is marginal), and Microsoft Corporation's decision to discontinue further development on Mac IE, we are unable to continue support for that browser.
Because IE/Mac does not fully support Cascading Style Sheets for positioning, rendering of layouts in these pages is degraded in IE/Mac. As we continue to migrate toward CSS-P coding standards, pages based on those standards will render poorly in IE.
In June of 2003, Microsoft Corporation officially discontinued further development of the Macintosh version of Internet Explorer, recommending that users switch to Apple's Safari browser, which is present on Mac OS X computers by default. Or switch to the latest version of Netscape, or any Mozilla variant (we recommend the excellent Firefox).
Robert J Crisler
Manager, Internet and Interactive Media
321 Canfield Administration Building
University of Nebraska-Lincoln