Wandering Trader Llamas spawn without Wandering Trader but has a lead.

I meet some Wandering Trader Llamas from time to time and I sometimes see the llamas without a Wandering Trader, but they are actually on a lead. I can name the llamas,but I can't ride, customize, or attach chests to them and when I kill them, they will drop their lead. I believe that it is a bug and if you can fix this problem, I will be very pleased.