This was also a problem for me. I have version 3.5.1 but I cracked the code to this frustrating problem in five easy steps.
Step 1. Select the picture that you want to have multiple pic's views.
Step 2. Click edit, and then scroll down to Product Gallery, below the title is a link "add product gallery image". click that link.
Step 3. From the add product gallery image screen click upload files, and then select your pic or pic's click open. (The pic's are now loaded to the product gallery.)
Step 4.Click the add to gallery button.
Step 5. Scroll up and click update. That's it, now click view product and all of your pic's are visible.
Also an easy fix if you have included the wrong pic or more than you wanted. You can easily delete that pic from the add product gallery image section. Click on the pic you want to remove, an X will appear to delete, click and the pic will be removed.
Hope this helps, Thanks