Yes, I see the same behavior in IE6.  I performed the following steps:

 

1) Leaving "Use Relative Urls" selected and the Cindy Crawford image in the editor, click the "Page Properties" button.

 

2) Enter http://sony.com in the "Base location" field.  Click OK.

3) Flip to HTML view and you'll notice that the src for the image has been changed to http://sony.com/uploads/Cindy_Crawford.jpg.

4) Clicking submit shows that http://sony.com isn't stripped out on the postback either.

I also noticed that on postback the editor loses my "Base location" setting.  Should it have preserved this setting?  I also tested the above steps in Firefox 1.0, and the editor would not even keep my base location setting.  I appreciate your quick responses on all of these posts.