As described here and in subsequent messages:
When clicking "View/reply online" in a digest, and then clicking "Like", it sometimes causes a draft to be saved. I could not repeat this all the time, but does sometimes create a draft.
I suggest two things:
1. No draft should be saved when the "reply" field is empty.
2. The "View/reply online" link in a digest should be just "View online", and should go to a page that shows only the message (without automatically opening a reply field). It is obvious that you can reply online because there is a very clear "reply" link when you view the message online.