Hi,
Thank you very much for the details, it helps us a lot!
This is a very intereting issue. I logged in and tried a few different things, and it turns out when the plugin requests the post content, this text is actually returned. I have made a few changes too to see if using different methods would work, but every single time this is returned as the actual post content.
My guess is, that the fusion builder may work differently during the actual page request and within the ajax request. To save resources developers tend not to initialize parts of their plugins during XHR requests (to make it faster), and I believe this is exactly what is happening here. Basically some parts of the fusion builder are not hooked up, so it does not execute the content filters and simply the default text is returned when requested.
I tried to look up their documentation if there is any way to explicitly force the page builder to initialize as in normal requests, but I found nothing. I also looked up all option, no luck either. I am almost certain this is a bug in their plugin, I highly doubt this was intended to work this way.
My best advice here is to use the advanced title and content fields feature. That allows you adding custom fields contents to the live results list, so you can replicate the fusion builder output to some extent.