Here's the problem:

My notification scheme is set up to notify current assignee on "Assign" and "Comment" events.
If I assign an issue to a user with no comment, then notification is delivered. But if I assign the issue and include a comment that is not visible to the assignee, the notification is not delivered!

I am guessing you're considering it as one event, and since the comment is not visible, choosing not to deliver the notification at all. This is bad for us.