I actually have a similar problem. I have a page with multiple radio buttons; each button will set the title and description meta tags of the page, via JavaScript upon change.
For example, if users select the first button, the meta tags will say:
<meta name="title" content="First Title">
<meta name="description" content="First Description">
If the user select the second button, this changes the meta tags to:
<meta name="title" content="Second Title">
<meta name="description" content="Second Description">
... and so on. I have confirmed that the code is working fine via Firebug (i.e. I can see that those two tags were properly changed).
Apparently, Facebook Share only pulls in the title and description meta tags that are available upon page load. The changes to those two tags post page load are completely ignored.
Does anybody have any ideas on how to solve this? That is, to force Facebook to get the latest values that are change after the page loads.