I was whispering a friend back and forth, and I would have a reply line typed out, with their name showing in the target field, and it would suddenly change the channel to Global and if I didn’t notice in time/was typing fast, I’d accidentally send it there instead of direct to my friend.
It seemed to happen when my party changed by someone joining or leaving, but this could have been a coincidence. I didn’t want to test extensively and spam either my friends or Global chat, but it happened to me three times this evening. All were /r replies and not new whispers.