It's not a bug, but it's due to how the legacy Horizons bios work. Of those, you can find more than one on a planet. Although the different variants are just palette swaps like Odyssey's variants (Cactoida Vermis - Red / Green / Blue / etc) are, they aren't variants, as they had different temperature requirements that the variant system couldn't handle.
For example, Roseum Brain Trees require a surface temperature between 200 K - 500 K, while Lividum, Aureum, Lindigoticum Brain Trees, all of which are just different colours of the original Roseums, require 300 K - 500 K instead.