I sometimes have an issue where I launch a command using a Google Now, and it asks for follow-up info (for instance, "What's the message?" when my command was "Send a message to xxx"), but it doesn't start listening for an answer. I can still click on the blank field on the screen and type in my answer, but it kind of defeats the point of voice commands.
Note that it's not systematic: sometimes, the voice recognition will indeed turn on and I will be able to speak my answer.
Is this a known problem, and if so, is there a way to fix it?