Jumping away from search box

Hello,
Out of nothing the following happened to https://www.bcgeldrop.nl
When you click in the search box widget, 1 second later you are redirected to a page.
And when i unpublish that page, a click in the search box leads to a 404 page.
Theme is Pagelines.

It only happens in Chrome and Firefox, no problem in IE!

Any idea what may have caused it? I haven’t installed any plugin recently.

Rob