Messages are encrypted for removed MUC members

Versions

OS: Debian GNU/Linux testing (buster)
Gajim version: Latest commit on messagewindow branch
GTK version: 3.22.29
Python-nbxmpp version: 0.6.6
OMEMO plugin: 2.5.13

Steps to reproduce the problem

Create a MUC, add members, enable OMEMO, send some messages, etc.
Remove a member
Send a message

Expected behavior

Message should only be encrypted for current members.

Only fingerprints of current members should be shown in the fingerprints menu.

Actual behavior

Message is also encrypted for removed MUC members.

Fingerprints of removed MUC members are shown in the fingerprints menu.