Like it says on the tin. I'm not sure exactly how it decides what species the new pop will be, but I've even had it give me a species that wasn't yet in my empire. I settled near the Drath during a war, and then manufactured several Drath citizens, who hated my guts.
My homeworld of Iconia is almost entirely filled with Arceans now. They were closest to me, we fought a lot, and almost from the time of our first war my pop assembly at home has been overwhelmingly Arcean. As I write this, Iconia has 2 Yor and 22 Arceans.
This is especially bad because as Yor I'm not allowed to build food improvements. So I have an ever expanding pool of organics being fed entirely on captured food sources.
This is definitely a bug. You're only supposed to receive Yor citizens when building pops as Yor. You should consider uploading a save file somewhere online and linking to it here, or posting in the Discord server here: https://discord.gg/bDZgQuGSIf you use the Discord, the Galciv4 section's sitrep channel or bugs-typos-goofs channel would be best for sharing this bug. Make sure to note what version of the game you're playing. You can either get the full build number from the Epic Launcher or at least provide the version number at the bottom of the main menu screen.
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