UNIX vs Windows LC CTYPE and UPPER mu

Hello,

first: i hope im right here in this mailing list.

My problem:

We have several Postgre servers 9.0.4, one on Windows Server 2008 R2 and
others on different UNIX/Linux systems.
Windows: LC_CTYPE = 'German, Germany'
UNIX: LC_CTYPE='de_DE.UTF-8'
(so LC_COLLATE is too)

on both systems
ENCODING = 'UTF8'

Now the function UPPER('µ') works right on Windows, giving me 'µ'
(unicode = 181 respectivly U+00B5).
On Unix I get a char like M (unicode = 924 respectivlyU+039C), the GREEK
CAPITAL LETTER MU
But we are not in Greek.

Is this a Unix based problem with a wrong local setup (we dont think so,
servers local working on other german letters like ä, ö, ü and UPPER too),
or a Unix local problem in principle,
or a wrong postgre server setup,
or a postgre bug?

Or is this a feature, not a bug.

We dont know where to search or where to fix something.

Thank you for concerning,
Dominik