I am not sure if this will be helpful. I added the element aa and bb to document and jquery height returns the right result. http://jsfiddle.net/dekajp/ugvGv/6/ (tested in chrome)

and the documentation of height says "Get the current computed height" - http://api.jquery.com/height/

This doesn't seem like a bug to me as what you achieved with jQuery works the same using only html.

You can check the html markup changes here http://jsfiddle.net/ugvGv/7/

The container <div> has a font-size set in 'pt' unit, and by that all the child elements height are affected when using 'ex' unit for its height.

ex = one ex is the x-height of a font (x-height is usually about half the font-size)

Getting style information on disconnected markup is dicey. That's particularly true since many inherited properties won't be available from the document on disconnected markup. I'm inclined to mark this wonfix since the "fix" is to attach it to the document before doing these measurements and it's better for you to do that.