[jitsi-users] Openmailbox password problem in Jitsi

I had a problem connecting to Jitsi with an openmailbox.org XMPP
account, on Linux.

When I first added it I got a message of "cannot validate certificate"
and then consistently the password was refused as invalid.

Then I tried:
1/ adding to Jitsi other XMPP accounts not from openmailbox.org. It
worked fine.
2/ adding the openmailbox.org XMPP account to other clients. It also
worked fine.
3/ different versions of Jitsi, uninstalling and reinstalling them: 2.4
stable, 2.5 stable, 2.5 nightly, same problems.

The problem then seems to be with the combination of openmailbox.org
and Jitsi.

Can anybody replicate that and suggest a solution?