Thanks. That is a handy tip I didn't know about :-)
It doesn't solve the Alt Text issue though, as the description would not be used in cases of screen readers etc.

As long as I don't have a pop up image I can add appropriate Alt text. As soon as I want a pop up and add Alt text it is displayed as a caption whether I want it or not. The display cant be turned off.

It's got me scratching my head this one. I really don't know what to do for the best.