Nested Accordian Collapse/Expand Issue (IE8)

jQuery UI encounters an error when you have an accordian whose content panels contain an accordian (nested accordian), and you try expanding the different content panels of the nested accordian.

Error Message = "Invalid Argument"

Location of Thrown Message = jquery-ui-1.8.20.custom.js (using unminified default smoothness package in this example) line 4920

Statement Throwing Error =

jQuery UI encounters an error when you have an accordian whose content panels contain an accordian (nested accordian), and you try expanding the different content panels of the nested accordian. 

Error Message = "Invalid Argument"

Location of Thrown Message = jquery-ui-1.8.20.custom.js (using unminified default smoothness package in this example) line 4920

Statement Throwing Error = 
{{{
options.toShow[ 0 ].style[ settings.prop ] = ( percentDone * showProps[ settings.prop ].value ) + showProps[ settings.prop ].unit;

Occurs When = Right side of statement evaluates to "-1px"

To Reproduce = Download test code from http://sdrv.ms/KO1seV, run in IE8, and expand the first nested accordian's content panels.

Additional Comments = Removing the jquery ui css styles causes this issue to go away. Changing the padding (or other values that affect height) in the jquery ui accordian css causes the problem to shift around.