OK, this is driving me batty!
I installed Membership and found that captions stopped working on some of the sites' pages. I then deactivated Membership, but the image captions still won't work! I don't know if this is Membership related, but it was the only change that took place at this time, and I am at a complete loss...
If you take a look at this page, you will see the image captions made using [caption] working correctly:
If you take a peek at this page, you'll see two copies of the same image. The first one, with no CSS formatting whatsoever is added to the page using [caption].
The second copy of the image is surrounded by a div with the styles coped from the theme's style sheet.
I have never seen anything like this! How can the css work correctly on some of the pages, and not work on others?