Hi @carofitz,

The Hide Grades option hides grades that have already been posted, but does not affect grading you do after clicking the Hide Grades button (that's what the posting policy does).  What you want is to change the posting policy for the assignment to Manual, which you can do by following the  How do I select a grade posting policy for an assi... - Instructure Community - 574  guide.  That should get everything to work as you'd like the next time you need to do this!

-Chris