from an experienced user:
This statement found on Facebook Developer might have something to do with it:
We don't recommend the Share button for new developers. If you aren't already using the Share button, we recommend you use the Like button and Open Graph protocol instead of Share for sharing pages from your website. The Like button is simpler to user and is the recommended solution moving forward.
Like when FB dropped the "Fan" button, it looks like they're moving everything over to "Like"...