Taming wild Llamas works fine. The problem is when you tame a llama, all of the llamas that become part of the 'caravan'.

You can sit on these llamas, but you cannot view their inventory because technically they are not 'tamed'. Because you can sit on them, you cannot tame them either. Basically if you find a pack of llamas you can only use one of them because the rest get stuck in this 'in-between' type state.