It would be better if you could post a screen shot ...
Click cursor on an image in the Library Grid view will show that image in Navigator.
but Hover the cursor over a thumbnail in the Filmstrip (or anywhere over the folder panel) and Navigator will show the image under the cursor.
So do not leave the mouse cursor placed above the filmstrip or folders panel- may be an answer.
And to change this 'feature'- Right-click on a Filmstrip image- select "View Options"- Click the option "Show Photos in Navigator on Mouse Over" to 'Toggle' it on/off with a check mark.