By that I mean, there is no space reserved for where the image should appear - just nothing.
I tested several methods.
I highlighted the image and selected "Align Center" from the editor buttons. It centers the smaller image on the page as desired, but on the front end it disappears when I refresh the page.
I removed the link from the small image to the popup, saved, refreshed the front end and the image returned.
I moved the small image on the page back to align: left, and after linking the popup the image appeared on the front end along with the popup.
I then opened the media box settings for just that small image, selected "Not Set" and changed that to "Centre" (yes, center is misspelled in the editor). That centered the small image, but the image disappeared on the front end.
I removed everything relating to the left / right positioning of the small image and added a class tag to the <p> tag in which the image was placed. I then added CSS in my main template to align that 1 image (text-align: center).
Low and behold, "that" worked!
So no matter how I attempted to center the image on the page (linked to the popup), it would disappear using any of the "typical" methods of alignment. But adding a class tag and using CSS on the <p> tag works.
You know JCE inside and out and probably already know what's happening.
It seems to be a bug - for me. For those not as adept at CSS, it may be cause for more serious pleads.
Thanks.