Problem:

$('<div><span>test content</span></div>').clone().html() returns <SPAN jQuery1219427608203="null">test content</SPAN>

and on the

...var id = elem[ expando ];.... line id value is "null" it may be null.

Solution:

I have debugged jquery and found the solution.

this[ expando ] = null; is not correct for ie. Please use the this.removeAttribute( expando )