Twitter Phantom Unfollow Bug

Noticed something strange when viewing a twitter page on the iPhone mobile view. There was a blue oval-looking button on the screen:

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When I clicked on it, I was shown a dialogue window asking me if I wanted to unfollow the account I was viewing. This was completely unexpected. As can be seen in the image above and the image below, I’m not signed into Twitter. So how can I unfollow someone, if I’m not even signed into an account?!?

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On click of Unfollow, the Sign in screen is presented to the user.

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The correct user behavior would be to not show a button to unfollow if the user is not signed in. If anything, the user should see a Follow button that should activate Sign in on click if the user is not signed in.