looks like it comes form this HTML:
<form style="width:100%; margin:0 0 0 0; border:0; padding:0 0 0 0;" method="get" action="/s/ref=nb_sb_noss" name="site-search">
Did it happen multiple times, or only once? If only once, i dunno why it would do that, but if it always happens, the sites server may be misconfigured and can't understand the URI.
Someone that knows HTML better than me could probably tell you what's up. But I'd say that it's harmless, and a fuck up somewhere on amazon's side.