No alliance leader?

[unmerged(9338)]

When I as Norway try to ally Mecklenburg (and their North German alliance), the "join alliance"-button is greyed out saying that Mecklenburg (!) is the leader of the alliance, and that I have to ask them before being able to participating in the alliance. The problem is: This is exactly what I am doing...

 

[unmerged(9146)]

Which patch are you playing? In the old patches this would happen if Mecklemburg didn't have diplomats, but I believe this has already been fixed.