CryptoUtils::copyHeader uses a wrong function to copy the header data.
it uses fromUnicode(asUnicode), but kmime_headers.h states:
"It is not guaranteed that fromUnicodeString( asUnicodeString(), ... ) will return the original string."
I run into this bug where the From and To Headers contained data such as:
"some name (bla)" <mail@a.b>
but asUnicodeString() did not put quotes around "some name (bla)" so parsing did not work out and left the result empty.