Primary Species change due to psionic awakening in xenos pops?

I was playing a xenophobe pacifist spiritualist race going the transcendance route. Everything going great, the only xenos in my little empire being two refugee pops from the subterranean empire. They gained latent psionics in an event without an issue, but when they became full psychics the primary species of my empire just suddenly turned to them. It doesn't make any sense - I have 215 pops and only two of them are of this new primary species. Is there any way to change the primary species back, or does anyone have any idea why this happened?