[ubuntu-uk] Problem with one mailbox in Thunderbird

[Dianne]

I'm running Thunderbird 38.2.0 on Ubuntu 14.04 LTS. There was an update 
to tbird last week, which seemed OK.

I have four email accounts that I download with tbird - my ISP allocated 
mail, my yahoo mail, and two email addresses on a server from a place I 
volunteer, and one of these has a major problem - every time I change to 
another mailbox, or close tbird, everything in the Inbox disappears. 
None of the other three mailboxes have this problem, all other folders 
(such as deleted and junk) are OK. I've made no changes to settings or 
properties - for retention all are set to follow account settings, which 
are set to leave on server (so I can at least look at the hideous 
webmail interface to see them), but our server will only keep them for a 
month.

Anyone else had a problem like this?
TIA
Dianne