QxtMailMessage does not preserve space at start of lines

I tried to format my message in text/plain and retreived contents via rfc2822 method. unfortunatelly all spaces from start of each line were removed.

in generated contents I see content-type: text/plain so it's handled as text and spaces should be preserved.

I've also checked RFC 2822 and thunderbird behaviour on this case. rfc doesn't notice anything about spaces in message body and thunderbird preserves them.