[Djigzo users] Charset problem on the reply site

Hi everyone, I have a strange problem with my djigzo 1.3.1 virtual appliance. When sending an encrypted email with german Umlauts in the subject, these chars are not displayed on the reply site. The email itself and the encrypted pdf file are totally OK. Everything is displayed as it should be, but as soon as I try to reply, the Umlauts in the subject are replaced with "?". The reply site itself is displayed correct with Umlauts (max. Größe). Can anyone give me a hint what I could do to solve the problem? Thanks and kind regards, Benedikt