[MlMt] Attachments column keeps disappearing

[Randall Gellens]

I've noticed that the 'Attachments' column vanishes when I switch to a 
different mailbox and then back.  Mailmate 1.13.2 (5673).  Is this a bug 
or a setting I've gotten wrong?  I use View->Columns->Attachments to 
turn it on, but it gets turned off when I switch mailboxes.

--Randall