Thumbnail Images: Only one image on a page can be viewed one time

Create a page with a thumbnail image.
Save the page.
Click on the thumbnail to view the full-size image.
Click again to go back to thumbnail.
Click a 2nd time on the thumbnail.
The thumbnail will not enlarge.
Click refresh.
Click the thumbnail it will enlarge.
Click the thumbnail again. It will not enlarge.

Users must refresh their screen if they want to see more than 1 thumbnail image more than 1 time.