mutilated cgi script parameters on apache 2.0.44

hi,
the webpage starting the cgi looks as follows:
<form ACTION="/cgi-bin/telsuche.pl" METHOD="GET"...
here's (probably) the troubled cgi section:

$query_string = $ENV{'QUERY_STRING'};
($nname,$telefon,$org) = split(/&/, $query_string);
($dummy,$nname) = split(/=/, $nname);
....
$nname = ucfirst($nname);
$nname =~ s/%([\dA-Fa-f][\dA-Fa-f])/pack ("C", hex ($1))/eg;
....
$select = "exec stp_TelefonSuche '$nname','$telefon','$org'";...

The script connects to a database an starts a stored proc with the 3
parameters.
Everything works perfectly when the $nname doesn't contain any german
umlaut. If it does the script stops and apache writes an error message
like the following:

....DBD::Sybase::st execute failed: Server message number=105
severity=15 state=1 line=1 server=WUEDMS1text=Unclosed quotation mark
before the character string 'L??:???????????^A.^A..'. at
/srv/www/cgi-bin/telsuche.pl line 85., referer:
http://wuedev1.reg-ufr.bayern.de/reg-ufr/telefon.shtml

where 'L??:???... is the mutilated $nname Parameter.
There's no problem at all running the script from the command line.
I guess it must be a problem with apache.