CK Editor: switching between source and wysiwyg is not working in IE 8

Reproduction path:

• Login in the current 7.9 CMS demo environment with IE 8
• Create a new document with a richtext field (e.g. a news document)
• Add some text in the rich text field
• Click on the source button, you will see the html source code
• Click on the source button again to go back to the wysiwyg interface, this is not working.

This was reproduceable on Virtual PC, Win7 - IE8.

It produced a javascript console error "Can't move focus to the control because it is invisible, not enabled or of a type that does not accept the focus"

See screenshot