What’s this =?ISO-8859-1?Q?Test13?=

I used my weblog for moblogging with pictures. Sending my story with a picture as email was no problem in 1.5 with an alternative wp-mail.php (wp-mail 0.312 by John Blade). Now in 2.0 I can’t get it running. Everytime the subject looks like this “=?ISO-8859-1?Q?Test13?=”, where it’s ment to be “Test13”. It drives me a little crazy, so how to solve this?