Robot pops will make your new non-robot pops have less/no ethics

I assume this is a bug, and boy was it not obvious what was happening. I am playing a Fanatic Collectivist/Materialist empire, and was very surprised to see my new pops spawning with different ethics on my colony worlds. I first noticed because some of the new pops were unhappy due to slavery (which none of my pops should be, due to fanatic collectivist); some had spawned with regular collectivist, and some with no ethics at all! My ethical divergence was negative, incidentally- and yes, I know there's a bug related to this as well; that was what I thought was happening. Not so!

I started purging, trying to get new pops with my core ethos. I ended up purging all but one pop, which I ensured had my ethos. Now, every new pop spawned with NO ethics!

Then I noticed- I had three robot pops on the colony, and robots have no ethics. Hmmmm.. I disassembled them all, and ensured the only pop remaining on the planet was the one with my empire's ethos. Ureka!

Now, every new pop spawns with the correct ethics. My guess is that the logic for new pop ethics looks at ALL pops on the planet, INCLUDING robots, to decide what the new pop has. Since robots have no ethics, new pops won't have any either.

Hopefully this helps someone else surprised at how their conformist collectivists keep changing ethos!