I almost know how to create a new races without messing up.
I don't recall this happening to me last time I made more than 3 races into Sins, and I am doing the steps as I recall before. I took a look at the new race mod and Zombie's new race guide, and it simply tells me to do what I've already done.
So I get a new race into the game to test out a portion of a mod I intent to help someone else out with, and when you scroll to that new Empire, you are forced to scroll backward to continue. You can scroll backward away from it. Putting the race in high or low priority does nothing for this glitch I seem to be experiencing. Additionally, I do have playerthemes and playerpicture dummies (of advent) set up, and placed in the manifests, as well as full entity and brush manifests counted for. I do have the Valid list in GalaxyScenarioDef for themes and pictures updated with the advent dummies, as well as playerTypecount in GalaxyScenarioDef updated. There are many other steps I've taken, but this is all I think is necessary to produce a 4th+ race without glitch, or am I wrong?