I really don't think there should be any reason. JFBConnect doesn't really do anything in the admin area of your site, and EasyBlog (I think) does it's auto-posting from the admin side, not the front-end side... so, there really shouldn't be a conflict there. As for 4.2, we added the Autotune feature which can change some migration settings. The only one of consequence (that I can think of) is the "Stream Post URL Security" setting. We recommend Disabled as that allows you to post any URL to your walls. If it's enabled, any posts *must* be derived from your App Site URL.. so, check to make sure that isn't enabled somehow.
We're getting more people talking about EasyBlog, so it's something we'll be evaluating for tighter integration as well as more testing with in the future. That doesn't help now, but your feedback on what you're using is definitely useful.
Thanks,
Alex