I've been downloaded the latest build of jQuery UI (1.9 m4) to see if the new redesigned accordion have the same problem or not, actually it have!
jQuery: 1.4.4 - 1.6
jQuery UI: 1.8.10 (probably previous versions are affected as well) - 1.9m4
Browser: Google Chrome 11.0.696.68, IE 8.0.6001.18702IS
Windows: HP OEM XP SP2 (fairly updated via auto update)
The only thing you have to do, is open any of the attached demos of accordion in the above browsers, then use the browser's zoom feature (ctrl+mousewheel for example), you can also refresh the page but it doesn't matter. Let's start clicking/switching on the accordion tabs and open them one by one, you will notice the height is continously change. As far as i tell, in google chrome the accordion tabs will grow, and causing the accordion object to grow as well. In IE8 you will notice the opposite behaviour, so it will shrink somewhat.
Using the Fillspace accordion demo, you can fix the height problems by resizing the object, but it will grow/shrink again if you start switching between the tabs.
You might also notice that the tabs widths are also somewhat messed up, so it will be a smaller width in chrome, and might be larger in IE8 than it should be.