it's a problem with encoding, you have to encode all "problematic" charachters (ö,ü,ä,ß...) with
&xHH;
where HH is the unicode-hexadecimalvalue of the character, so for "die purpurnen Flüsse" you must search "Die purpurnen Fl&x252;sse"
unfortunately i can't do anything about it, it's a site issue