My problem is similar to this, only I couldn't get a solution from that discussion. I'm building a page with FB connect, and I need to post something to the user's feed. If I click the button I created for it, the feed popup displays correctly, and I can post to facebook. However, if I navigate to another page or if I refresh the page and then try again, then the popup won't show. There're no errors in the console. If I log out of facebook and then try to publish again, the popup will show one more time, and then stop working.
EDIT I think it's fixed - by adding the property: display: "popup" I was able to make it work every time.