There is a bug with "Take Mandate of Heaven" CB.

[Piotrzeci]

I was wondering what would happened if two nations declared a Take Mandate of Heaven War on the Emperor and demanded it in a peace deal. In opposition to CK2 Eu4 does not stop wars if CB is lost. I decided to use tag-switching and declare two wars on Ming: as Oirat and as Jianzhou. Then I sent two peace offers both demanding the title of the Emperor. After accepting the first offer the result was:

As you can see the second peace offer is still floating around even though Oirat is the new China guy.
One click later and:

Then I checked possibility of accepting one offer and then sending the next one, but this option is not available (as it should be)

It's not a huge problem, but someone will eventually have it in their game and stealing MoH without going to war with the current Emperor could be frustrating.

 

[Piotrzeci]

It's worth noting that at the time of 3rd screen Jianzhou isn't the Emperor anymore. I simply truce broke as Ming and took it back (as Haixi and Korea were not able to use take Mandate of Heaven CB for some reason). I basically did the same thing. Were able to steal it with Yeren, but after accepting peace offer from Ming (Me-ng heh) the option is not available anymore.