it's likely Windows command line processing (maybe caret is used for control characters, ie ^G == Ctrl-G). try putting single or double quotes around the option. you may also be able to '\' escape the caret. it works fine under linux.

$ perl test.pl --str=$%^@*jimbo
$%^@*jimbo
$ perl test.pl --str='$%^@*jimbo'
$%^@*jimbo
$ perl test.pl '--str=$%^@*jimbo'
$%^@*jimbo
$ perl test.pl --str="$%^@*jimbo"
$%^@*jimbo
$ perl test.pl "--str=$%^@*jimbo"
$%^@*jimbo