Vassalization of Overlord

[Squazl]

So I was playing as Wallachia today and decided to No-CB and vassalize Byzantium to deny the cultural union for the Ottomans, but what I didn't expect is that I also got Athens as a vassal for free. I assumed that Athens would become independent.

I became curious and started a new game in normal mode vassalizing (through console) tags with multiple vassals and was surprised that I'd get all their vassals as long as they don't have more than 2. If they have more than 2 vassals I'd get a little more than half of them. Example Muscovy, Beloozero and Yaroslav become independent. It seems to randomly decide who changes overlord and who becomes independent, but it's not random because it's always the same result.

My questions are:
1. Is this intentional?
2. Which patch introduced this change?
3. How do I know who becomes my vassal before I vassalize a nation with more than 2 vassals?

 

[bradles0]

3. How do I know who becomes my vassal before I vassalize a nation with more than 2 vassals?

I would check for either the highest or lowest development, or the lowest liberty Desire.

 

[Squazl]

I would check for either the highest or lowest development, or the lowest liberty Desire.

That doesn't appear to be the determining factor. If you vassalize Muscovy you get 26 dev 45% LD Perm, 8 dev 34% LD Rostov and 20 dev 45% LD Pskov as vassals and 17dev 35.8% LD Yaroslav and 12 dev 35% LD Beloozero become independent. Even vassals with development over 100 or LD over 100% can get vassalized for free.

 

[Squazl]

3. How do I know who becomes my vassal before I vassalize a nation with more than 2 vassals?

I just noticed, that if you go on the diplomatic window of Muscovy the vassals are listed in this order: Pskov, Yaroslav, Perm, Beloozero, Rostov. You get every odd vassal. At first I didn't think this was the answer, so I tested it on Ashikaga but it is indeed the process that decides your future vassals.