There is a problem with jQuery when content type is set to "application/xhtml+xml".
Nick has submitted a bug to jQuery long ago, but they just don't care, so it was fixed in RF 3.3.x (or ealier) by additional code in jquery.js bundled with richfaces. This code is not any more in RF 4.0.0-SNAPSHOT. Shouldn't it be added?
It's this code: