Andy,
JFBConnect shouldn't be doing that, but we've been caught doing naughty things in the past (on accident, of course). To rule us out is very simple though.. disable the JFBCContent and JFBCSystem plugins. That effectively disables everything JFBConnect do on your K2 (or just about any other page). If the description is still incorrect, you know where not to look.
In general though, the general meta description tag is not something we modify at all. JFBConnect only sets the Open Graph tags, and while we'll look at the meta description tag to possibly use that for an OG tag, we shouldn't be setting that tag.
Hope that helps, and keep us posted on what you find,
Alex