Yesterday I started seeing a strange sliding window appear on my iPhone 5 whenever I went to compose a new message or email, or add a new contact. (See image at right.)

After much frustration and searching I eventually discovered that this is the “Window Zoom” functionality, part of the Accessibility settings, and it enables you to enlarge parts of the screen to make it easier to read.

It seems that at some time I must have accidentally enabled this feature, and once enabled a three fingered double tap (intended or accidental) will cause the sliding zoom window to show up in various places.

The solution was to simply disable the “Zoom” function in the Accessibility settings.