Deleting messages interfers with top message

[Michał Karnicki]

Steps to reproduce:
1. Create chat
2. Add a person to the group
3. Remove a person from the group
4. Last message should now be action message about removing the person.
5. send a message
6. From different client (Android), remove the last message

What should happen:
Dialogs list should show the last action message (foo removed bar)

What actually happens:
Dialogs list shows: "foo:"

When I re-launch the app, the state is correct (so the state in the db should be correct, perhaps the model is not being updated properly on message deletion).