This plugin is extremely simple yet useful, and I highly recommend it.
It inserts text/html at the end of every post, BUT it also does this for post excerpts shown on the home page.
In my case it was unreasonable to have multiple instances of social sharing buttons with all scripts and overhead on the home page given that the user does not see the entire post and is not expected to share it this way.
I had to add a few lines (
add_filter('get_the_excerpt'...) and now the plugin works great - it adds social sharing buttons only when the users open the posts, but not on the home page.