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.