Fixed in HEAD and 4.0.4.

It would make more sense to check if the message is a 
multipart/alternative message, and enable HTML composing with the 
text/html part in this case.

I stepped through what I thought was the code path for this.  Unless 
I'm mistaken, the problem appears to be that when the message is 
reconstituted, the plaintext part is always used, and somehow the HTML 
part is either ignored, silently discarded, or inaccessible in the 
Compose screen.  I'd propose a solution that would look to see if 
compose_html is set and if it is, return the HTML portion, otherwise, 
return the plaintext.

If you are in HTML composition mode in IMP, and you save your message 
as a Draft, the HTML code is preserved in the Draft folder message.   
However, if you resume working on that draft at a later today, all the 
HTML code disappears when you load the draft.



Simple test:



Create a one line message, with the word Test.  Switch to HTML mode, 
make Test bold and save as a draft.  Open the draft folder, choose the 
message you just saved and when you switch to HTML mode, your 
formatting is gone.