Sounds like you're not seeing the effect because you don't refresh or requery the form after the change. The clue is
When I begin navigating through the records I see the condition being applied
Moving off of a record is one of the ways to commit any record update or append without explicitly doing so in event code. If this isn't the case here, you'll have to elaborate as your description of the situation is a bit vague.
A simple way to commit your change could be something like IF Me.Dirty Then Me.Dirty = False
That can cause your form to automatically reflect the change, but as I said, not much info in your post to go on, so I'm not sure.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.