FWIW I get a JS error in IE when closing the Ext window with the chart panel.
I do not get an error in FF when closing the same window.
Page used:
http://dev.sencha.com/deploy/ext-4.0...arts/Area.html

Error listed in IE:
Line: 5513
Char: 21
Error: No such interface supported

IE used: 7.0.5730.13CO
FF used: 3.6.13