Personal Unions diplomatic capacity issue

[Smailus]

I am playing as Italy, which holds more than 1000 provinces in the late 1600s, and without trying I became part of a personal union with an OPM, which is unfortunately a vassal of Austria. I do not know how the calculation for diplomatic capacity works but this union with an OPM costs me 15 diplomatic capacity and keeps increasing as I get bigger, not my partner nation (it was and still is an OPM for more than 100 years). I cannot annex this OPM because it is a vassal of another country. I have tried to fight with Austria to cancel its overlordship, but as I have entered the war, this OPM suddenly became free, and as I ended the war it suddenly became Austrias subject again. I am stuck; I cannot exit this union without abandoning my dynasty. Please fix this bug, or make the calculation for diplomatic capacity in terms of the other partners in the union, not my own.

[eaerion]

Can't you make someone else a king of this country? There is a diplomatic option to do so. You will lose a PU but no other drawbacks.

[mikemonger]

If they have 100+ opinion of you, you can stick a relative of yours on the throne, which ends the PU. The option is on the PU screen or diplomatic interactions screen.