Kmail not syncing read/unread state with imap mailbox

I'm using Kmail 5.11.0 on an updated Arch machine.

I've set up this yahoo.it mailbox via Imap, the db has been set to 
PostgreSQL and it works well except from this annoying issue:

If I read mails from Thunderbird (on another machine) and then I come 
back to Kmail, messages I've just read are marked as non read. This 
happens even if I hit the "check for new mail" button.

Messages are actually marked as read by Thunderbird since their state is 
displayed correctly if I check those on the web interface of my mailbox 
or by k-9 mail on android.

On the contrary, reading mails on Kmail and then back on Thunderbird (or 
others), messages are shown with their correct read state.

I don't know if there is the same issue with madiaDB too since I managed 
to use PGSQL from the beginning.

I haven't find any solution/workaround at the moment, so if you can 
confirm this, I think it is a bug.

Thank you