You must misremember having made the mistake before, because whenever you land a new population, it creates a new colony just for that alternative species, so the mistake can not happen.
However, I tried again, just in case that previous colonies did somehow carry over the stats to the secondary. Nope, the criminal filth still 'rocks' the underground.
Documentary proof screen:
Maybe it is just a bad rounding problem? Gravity range is pretty close, however the F9 window clearly shows Tau'Kor here as starting with 0.05 indeed, yet the moon does not show colony costs. The asteroid of 0.09 is exactly on the lower limit of normal Tau, and they get the display just fine, despite being even sharper on the edge of the possible range.
///Edit:After Haji reported being able to colonize moons down to even 0.01g, I looked again closer. Well, nothing changed for me not being able to colonize the moon, but I noticed that a couple other moons around gas giants, who would normally have been outside of my range there,
do in fact work. 0.09 would have been my normal limit, but with the new race I see colony costs for 0.08, 0.07, and then... even a 0.05!
...So there
is a 0.05g moon that is colonizable for the new race, but the one right around my home planet -same conditions- is not?
How can that be? What is the deciding factor if not just gravity?