Switching between tabs in edit mode, loses changes in IE 6 and 7

To replicate issue -

1. Edit a page.
2. Type text in Rich Text tab
3. Switch to Preview tab and the text disappears
4. Switch back to Rich Text tab and text reappears
5. If user switches to WIKI markup - and switches back to Rich Text, the change gets lost permanently
   Finally, Saving the document loses all edited text from step (2).