Philip,
As you've seen in the past, we have no problem posting small code changes in the forums. Unfortunately, the code required to fix this was distributed across the main component, and both user and system plugins. It's a bit of code and also spans changes from the 4.2.3 release as well. It's simply not something we'd post because it would take a lot of time to pull it together, and it's affected by multiple other changes in each release (see our
changelog
for fixes related to logging in in 4.2.3 and 4.2.4), which means it may not work properly without some of the other changes.
This is one of those times where Facebook changed something and we had to push out a fix for it, and is a consequence of relying on 3rd party authentication.
However, with all that said, this only affects the auto-login functionality of JFBConnect. If you disable the auto-login option, you shouldn't experience this problem. It may not be the ideal fix for you, outside of upgrading, but it will at least prevent the problem for your users.
Hope that helps, and sorry for the troubles,
Alex