Incorrect absolute position of layer in Mac IE

[Andrew]

When I use layers I'm finding that they always appear about 150px to
low. This only happens in Mac IE.
Netscape and Windows IE work fine.

If I resize the window a little, then all the layers will appear in
their proper location. If the layer is visible when I resize it, it
snaps into place.

Here's my DIV tag:

<div id="mar" style="position:absolute; z-index:1; left: 20px; top:
100px; visibility: hidden"><img
src="/images/picture.jpg" width="200" height="200"></div>

Is this a bug in IE on a Mac or bug in my code?

Is there a fix?

Many Thanks
Andrew