Steps to reproduce:

Go to account settings, select "server settings" and change "message store type" from "file per folder (mbox)" to "file per message (maildir)".

Actual results:

All the column settings in the message list are messed-up. Some previously visible columns disappear, some previously hidden columns appear, the order of columns is changed. (I don't know, does it reset everything to the "default" settings or to some strange state.)

Expected results:

Only the backend (storage format) must be affected. The user-interface settings must be preserved.

By the way, the read status is also randomly reset for some (not all) messages.

Version 68 (ESR) seems to behave the same way as version 60 (ESR).

I have noticed that the conversion itself does not create .msf files in the destination. If I manually copy the old files there before restarting Thunderbird, then the column settings are preserved. However, the message read status is still messed up. Where is it stored? Can I also transfer it manually somehow? Since nobody cares to repair the conversion process, maybe I can at least repair its results on my system...

Version 78 (ESR) seems to create .msf files and apparently preserves columns, but the read status is still messed up.
I've noticed that it is also always messed up if I just try to "repair folder", either before of after converting (see my comment in Bug 1684016). Is this related to the problem?