Changes for bug #779804 uncovered a bug in the existing code, which was about not truncating output stream before re-saving the message due to changes (either the Date header or the From header), which could result into having some garbage at the end of the file (tail doubled). It didn't strike straight always, sometimes only after the second time the message had been viewed and for plain text message it meant to have doubled the end of the message text.

One noticed change was with line endings in message headers, where the MIME content of the message returned from the server used \r\n, but Camel resaved the file with \n (thus it was shorter by characters equal to header lines). There could be other changes related, especially when changing the From address.