Coalesced Corruption Demons always from Flesh Tribe

I'm in T8 maps and am now in my 5th corrupted zone (not map, but set of corrupted maps) - and every single map/zone always spawns the Flesh Tribe demons.

I think this is a bug? Isn't it suppossed to pick a tribe at random? Especially annoying because I've specifically just levelled this character to capture the Demon tribe in low level spectres for my "real" character