Plugin breaks markup/page by not properly converting double quotes

For example,

the plugin puts in the page code a tag: <meta itemprop=”description” content=”<p>Blah blah bla blah, bah blah, blah: “Blah, blah blah blah.“ Blah blah!</p>

The inner-quotes (bolded) break the markup, with unpredictable results, usually with very strange output.

It should convert quotes (you’re using esc_attr($post_excerpt) to generate this, I see) but it does not. Why? What am I missing? As it is now, the plugin is unusable when you have quotes in the post excerpt.

Thanks for your awesome plugins!

http://wordpress.org/plugins/wp-postratings/