I agree with you, but it looks like the module is skipped when the Google/Twitter redirect back. I guess that the IFBLogin module has assignments set as 'On all pages' based on what you said before, so this is weird.

Of course there could be some third party extensions/plugins interfering with this process. In this case that should be identified.

Only a suggestion for Twitter: try to set 'No' the parameter visible below and check if it fixes.