We have been opening a sharing popup (via window.open) with the URL like
https://www.facebook.com/sharer/sharer.php?s=100&p[title]=EXAMPLE&p[summary]
I review your url in use:
https://www.facebook.com/sharer/sharer.php?s=100&p[title]=EXAMPLE&p[summary]=EXAMPLE&p[url]=EXAMPLE&p[images][0]=EXAMPLE
and see this differences:
I use this URL string:
http://www.facebook.com/sharer.php?s=100&p[url]=http://www.example.com/&p[images][0]=/images/image.jpg&p[title]=Title&p[summary]=Summary
In the "title" and "summary" section, I use the php function urlencode();
like this:
title); ?>
And working fine for me.