Trader llamas do not join llama caravan unless a trader llama is the leader

There is an inconsistency with trader llama caravans. When I tie a lead to a normal llama, all other llamas nearby follow in a caravan as usual. However, trader llamas don't (and yes, I had less than 10 llamas during my testing). And when I tied a lead to a trader llama, all llamas, both normal and trader, followed in a caravan.