Hi Keith,
Thanks for trying out the plugin and sorry for not getting back to you on time.
The plugin doesn’t add the tweet and all other button in the post content. The buttons are appended to the post content when the WordPress loop runs. SEO plugins like Yoast usually use the WordPress post content which is what you type in WYSTWYG editor. So I don’t think the Yoast WP SEO plugin is picking up the tweet text from the plugin.
Also regarding facebook sharing I tried randomly on few posts on my blog but couldn’t reproduce the issue.
In case you happen to read this and you are still using the plugin on your blog I request you to please share a link to a particular post where this issue is happening so we that can debug further.