I have the exact same problem!
If I (or someone else) shares a post on my weblog the only thing facebook “sees” is the static heading text (which might come from a channel) and the static footer text.
Anything which is in the blogroll is hidden from facebook, regardless if I publish the roll itself or the one post.
(noted is that the “single post” page is in fact a blogroll, and perhaps that could be done in some other way?)
Nevermind my comment above, I solved my part of the problem with sending OG-metadata to facebook..
A complicated matter since I have a separate html-header page, but something like this:
In the html header:
<meta property="og:description" content="{embed:page_content}"/>
on the page itself:
{embed="embeds/html_header" page_content="{exp:channel:entries channel="patricks_blogg"}{exp:eehive_hacksaw words="50"}{exp:low_replace find="<p>|</p>" replace="" multiple="yes"}{entry}{/exp:low_replace}{/exp:eehive_hacksaw} {/exp:channel:entries}"}
Note that I needed to use both “ee_hive_hacksaw” to minimize number of words in the meta, and also “low_replace_find” to rempve tags until I got it working seamless.
/patrick