Stumped on way Instagram is working.

I think your message may have been cut off for some reason, but I'll answer the one question you have..

Usually, for any social network, the first time you login with your social credentials you have to give authorization for your website to connect to the user's social network account. After that first login, further authorization prompts won't appear when trying to login again. So, if you're already logged into Instagram on another tab and then hit the Instagram login button on your site, you'll be logged in automatically... no other prompts.

I hope that helps explain, but should you need anything else, just let us know.

Thanks,
Alex