When on the blank sitesearch (http://myhost01:8089/dosearchsite.action) , the easiest to reproduce this bug is: just press the search button over and over again. My search query ends up having lots of ", , , , , , , , , , , , , , , ".
It always extends the new proposed query field with the query text of the previous search. Happens in every Browser tested, so it doesn't look like a browser-problem to me; Firefox 2 and 3, IE 6

In general, search seems borked since 2.9. But that's another issue.