ajax make the filter(textfield) size changed

Hi,i have issue in content management,after i activated the ajax and add filter for user:name .
the position for textfield(search username) is correct in the right place,it changed after i click the "apply" button for the search,
i tracking that because ajax add size for the textfield,but the problem i cant find that ajax that set the size for the textfield.
need a guidance
sorry my english is bad
for easy to catch what i mean
please open this link
before: http://screencast.com/t/rNqijc45Rj
after : http://screencast.com/t/pkg4TAWbLpPy
Best Regards,
Randy