To reproduce bug:

I was playing as arabia, my friend as ottomans. LAN game. We had an ROP and an MPP for many many turns.

First, I noticed something weird: looking into t he Foreign advisor -> "Details" screen, I have 2 ROP and 2 MPP with Ottomans (!?!?!?!?)

Now for the crash:

Meet the ottomans, go in "active" to cancel one of the MPP. If you try to go in Active again, or see the Details in Foreign Advisor, the game crashes.

Savegame (even zipped) is too big to attach.. :(

so they didn't fix that in 1.27. Shhhhhhhh.t