jquery.placeholder is applied to all input elements with a placeholder class.
In IE, this causes .val() to return the placeholder string when it's supposed to be empty. It causes bug 47039 in Translate and may cause other issues.
As an experiment, I tried replacing the core jquery.placeholder.js with the
plugin of the same name from here:
Everything just worked, including the placeholder in the search box.
Of course, it needs more testing, and the whole thing may also have some other solution.