Thanks for your patience. Knowing that the issue was related to the EasySocial plugin helped us to narrow down the issue, though I'm still unsure of the cause.
The non-SEF URL is only created when the EasySocial profile plugin is enabled and the following line in the constructor is called:
$this->registration_url = FRoute::registration();
That line of code is simply asking EasySocial what the URL for the registration page of EasySocial is. All the code is within EasySocial for that call and something inside that FRoute call seems to be altering how the EasyBlog URL is generated later on during the Auto-Posting feature.
If you aren't using the "Registration Component" with a setting of 'EasySocial', you can comment that line out and everything should work as normal in JFBConnect and hopefully EasyBlog. If you are using the EasySocial registration flow with JFBConnect, you may need to bring this information back to StackIdeas to let them know the call that is happening before the AutoPost request that seems to be breaking the URL to understand how the 2 are related.
I hope that helps get you going,
Alex