Search for German Umlauts not working

[mkarg]

I already asked for help on the German user forum, but since nobody replied it looks it is a bug. So I'd like to kindly ask the developers to comment whether they think it actually is a bug:

I am using an external database which runs on ISO-8859-1, so I have configured:

SourceCharset => 'iso-8859-1',
DestCharset => 'utf-8',

German Umlauts show up absolutely correct in OTRS (e. g. a company named 'Zügel' is shown exactly as 'Zügel').
But when I want to search / filter for customer like '*Zügel*' I do not get any results -- until I am masking the Umlaut like '*Z*gel' which is an effective workaround.

So if this is my fault, please tell me where I could have caused that strange behaviour. If this is not my fault, please confirm that it is either a bug or wanted behaviour!

(viewtopic.php?f=35&t=25646)