UnicodeEncodeError in search_text field

OOPS-1725N43 was caused when the matching FAQ search failed, though the search for questions seceded:

   - /srv/launchpad.net/production/launchpad-rev-9771/lib/lp/answers/browser/../templates/question-listing.pt
   - Line 97, Column 4
   - Expression: <PathExpr standard:u'view/matching_faqs_url'>
 ...
   - __traceback_info__: (<zope.browserpage.metaconfigure.SearchQuestionsView object at 0x1048a090>, 'matching_faqs_url')
  Module zope.traversing.adapters, line 44, in traverse
    attr = getattr(subject, name, _marker)
   - __traceback_info__: (<zope.browserpage.metaconfigure.SearchQuestionsView object at 0x1048a090>, 'matching_faqs_url', [])
  Module lp.answers.browser.questiontarget, line 452, in matching_faqs_url
    'field.actions.search': 'Search',
  Module urllib, line 1267, in urlencode
    v = quote_plus(str(v))
UnicodeEncodeError: 'ascii' codec can't encode character u'\\xb4' in position 3: ordinal not in range(128)

PATH_INFO: /ubuntu/+questions
QUERY_STRING: field.search_text=can%C2%B4t+start+ubuntu&field.sort=RELEVANCY&field.sort-empty-marker=1&field.ac ... eld.language-empty-marker=1&field.status=ANSWERED&field.status=SOLVED&field.status-empty-marker=1