mailbox being modified

[Jean-Pierre Radley <jpr@xxxxxxx>]

SCO OpenServer 6.0.0.
Mutt 1.5.16

Something started happening a few days ago, and only for one particular
login for which I've always kept a screen open running mutt.

I leave that screen, and come back a bit later.  If I see a notice
that new messages have arrived, I down-arrow to see them.  They appear
*without* the 'N' indicator, and an error message says the "mailbox
was externally modified, flags may be wrong".  Any 'N' flags I've left
attached to earlier messages stick around; it's just the latest arrivals
that lose that indicator.

I'm logged in under the same user name on other screens doing nothing
related to mail; no one else is on the computer.

I'm really scratching my head trying to find out how the mailbox could be
modified.

-- 
JP
        ==> http://www.frappr.com/cusm <==