Llamas don't breed when a trader is near

I'm currently breeding llamas (trader llamas, to be precise); they've been breeding fine so far, but now they refuse to make babies when put into love mode by feeding hay. They accept the hay and show the hearts particles, but they won't pair up to procreate.

It's the first time it's raining since I've started the breeding project, so I blame it on the rain.

Update: Nope, it wasn't the rain. Turns out there was a trader nearby (with his own trader llamas). Now that I've... erm... shall we say, sent him and his llamas off to greener pastures... my llamas are breeding again.