WordPress version: 3.5
WordPress SEO version: 1.3.3
I did this: After installing the plugin I went to an article (on a test server) to test it. I set the title, keyword and description. I then went to Page Analysis and started moving through those items. One of them (an orange one) claims that I have images without alt text. So I went through and verified that all uploaded images in the WP media library have alt text specified. Then using firebug I verified that all the images have alt text defined on the page. I then forced a page refresh.
I expected the plugin to do this: I thought the orange alert would turn green.
Instead it did this: However, it stayed orange.
The page I visited is here http://www.temptales.com/bay-window-curtain-rod-diy-guide/
Have you thought about listing the offending images filename(s) on the page analysis?