Hi,
this happened now once more, so I considered to write it down: I start composing a new HTML email. Filling in a receiver, a subject, switching to body text area, deleting the prefilled signature and writing a line of text. Now I click send and get the German warning for: "Are you sure to send an empty email?" - clicking on yes sends the mail and opening the mail in the sent folder there is a text body. So I guess, there is something wrong with the body text check.