Cavalier Mount question
 

I am doing a Goblin with the rough rider feat. I selected a wolf with the cavalier archtype. I can't set it it to medium.

"You must choose an animal companion that's at least one size larger than you, but if the animal usually starts as Small, you can begin with a Medium version of that animal (changing no statistics other than its size)." APG 146

Looks like you can use the Size Category adjustment to increase the size to medium after selecting Wolf. This doesn't negate the error, though.

Submit a bug report if you could please, that's something that we should have functionality in for.