This can happens if you decode it twice.
Observe: http://3v4l.org/uK5a6
var_dump(urldecode(urlencode("((u.firstname LIKE '%Carol%') AND (u.lastname LIKE '%Enriquez%')")));
var_dump(urldecode(urldecode(urlencode("((u.firstname LIKE '%Carol%') AND (u.lastname LIKE '%Enriquez%')"))));
string(64) "((u.firstname LIKE '%Carol%') AND (u.lastname LIKE '%Enriquez%')"
string(62) "((u.firstname LIKE '�rol%') AND (u.lastname LIKE '%Enriquez%')"
%
is a special character used in URL encoding. %Ca
might be Ê