[Users] Reply fills From box with senders name(s) not mine

[Bob Williams]

Claws-Mail 3.17.8 installed from openSUSE repository on openSUSE Leap
15.2 and KDE Plasma desktop. Working flawlessly up till now.

I have several mail accounts set up, but one (the default) has been
behaving oddly recently. If I select any of the Reply options (Reply,
All, List, Sender) the From field in my reply gets populated with all
the addresses that the original message was sent to.

The account selector drop-down to the left of this field shows the
correct name of the account I am using. If I use this drop-down to
switch to another account, the From field gets populated with the
correct address. I can then switch back to the original account, and
now it shows the correct From address for that account.

This only happens in one account. It does not happen in this account if
there is a separate SMTP-only account setup for sending, which I have
done in several folders.

I suspect a file has got corrupted, but which one?

Any suggestions, please?

-- 
Bob Williams
   System:  Linux 5.3.18-lp152.50-default
   Desktop: KDE Frameworks: 5.71.0, Qt: 5.12.7 and Plasma: 5.18.5
   https://useplaintext.email/