imap access to videotron - annoyances

I am running Linux and Thunderbird as a mail reader. I have several email accounts at videotron, which I access

through IMAP. On one of the accounts several times a week it fails to connect and asks me if I'd like to input a new

password.

What I have to do is to logon to the videotron site, go to the email section and change the password on the failing

account to the same password. Then Thunderbird connects and get the mail. Videotron insists this is a problem

at my end...but it seems it's videotrons equipment which is somehow forgetting the password for the account because as soon as I "change" it to the same passwotrd, IMAP connects properly.

Problem  is the problem  is too technical for the Videotron people and they are not interested in solving it.