Treepanel and its filter freezes when the user keep it open for a while.

We are using a a treepanel and tabpanel almost the same way as the examples site. The filter works perfectly. But when the user keeps it open for a while such as going for a meeting, the filter no more editable. We where using HttpHandler type tree loader and session timeout in IIS is set to 300mins. Please suggest some workaround for avoid the freezing that occur while the browser left alone for a while..