sort=date-received messed-up after attachement deletion

[Louis-David Mitterrand <vindex+lists-mutt-dev@xxxxxxxxxxx>]

Hi,

after deleting the largest/useless attachments from my inbox I just 
noticed that all the affected messages now appear last in my default 
date-received sort.

As the headers have not changed (AFAIK) what does mutt use to change 
these messages' order? I don't see any additional/modified header that 
could warrant such a reordering. Could it be the maildir's files' mtime? 

I thought 'date-received' implied some parsing of the 'Received:' 
headers.

Bug or feature?

Thanks,


PS: this is with debian unstable's latest mutt 1.5.18