Assignment tool releases grades too soon.

I'm a TA. I've been doing some grading of student assignments that they have
submitted via the assignments tool.

When I finish examining a student's submission, I write up some comments,
give a grade and then hit save. I had assumed that the grades and comments
would not be visible to the students until I went through the step of
releasing the grades. However, I've had students ask me about grades I've
given before I have completed the rest of the class and hit the release
button.