Hi,
I've been having this problem since the editor was updated to WP 2.3.2
When I log-out and then login everything works perfectly okay. But, when I continue from a previous session (I'm working on my home PC, so no security issues regarding complete logouts/logins) the popup windows for image properties etc... in the WYSIWYG editor open up, but don't display the contents inside them.
I didn't have this problem in 2.3.1 so I thought that it might be a bug of some sort.