Floating keyboard on an iPhone?

An app store reviewer has rejected my build. With his message he posted a screenshot with a floating keyboard on an iPhone.

I know this feature only from iPad OS. How can I enable a floating keyboard on an iPhone?

Background: In this case I have implemented a MFMailComposeViewController as described in the documentation. No big deal, it works perfectly on all of my devices.

The reviewer claims that it will not work / not dismiss on his device, posting this weird screenshot.