With Search and German texts there is a problem. If I search for "ss" it finds "ss" and "ß". Results should be only words with "ss". If I search for "ß" (which also finds "ss" and "ß") results should only be words containing "ß". This is an annoying bug.
I don't see a problem here, this is intended behavior AFAIK. But others with more insight should decide how to continue. Erack, cloph maybe?
You have to check the option "Match case" to distinguish between them.