My vassal has a DP, but is at war too

[Tatran]

I've joined a PA with Cyrus a handful of turns ago.
Cyrus had a DP with Saladin, so I had a DP with Sally too. Nothing weird so far.
Team Cyrus/Tatran declared war on Germany.
Turns later team Cyrus/Tatran created a colony, Lincoln came into play
and became our vassal. He also had to declare on Bismarck.
But the picture gives information.
(Btw, nothing strange happened when I declared on Saladin, Lincoln simply
declared on him too.)

 

[alexman]

I don't suppose you have a save from just before Lincoln spawned, do you?

 

[Tatran]

All saves are gone.