Image Caption broken after 3.4

I’m currently using the Zack 990 theme (and have been for a year or so) but after the WordPress 3.4 upgrade, it seems any NEW posts, there aren’t any image captions on my site.

Example – https://www.ap-photography.com.au/blog/
First blog post (password is zack990) has no image captions. Rest of my posts display properly.

From doing some searching, it seems the shortcode for captions has changed in 3.4 But I have no idea what I need to change in my functions.php file for my theme.
And, the theme hasn’t been updated in a long time.

Is there an easy fix, or is someone willing to look at this?

Thank you.