One of the biggest changes to Samsung’s Galaxy S8 is the removal of the physical home button — a decision made in order to squeeze as much screen as possible onto the front of the phone. But S8 owners have noticed something very unexpected about the device’s new pressure-sensitive software button. It moves.

This movement isn’t particularly noticeable on a day-to-day basis, but if you stick something onto the phone’s screen as a reference point, you can clearly see the button shift back and forth, ever so slightly. These photos via Dutch site GalaxyClub show it more clearly:

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But why is this happening?

The best explanation (and one that’s been sort-of-confirmed by the Samsung Netherlands official Twitter account) is that the home button moves to avoid screen burn-in. This is a problem usually associated with old CRT monitors, and happens when a single image is left on-screen for too long, creating a permanent “ghost” on the display. This problem was actually what led to the creation of screensavers, the original use of which was to change the pixels on the display, preventing any static image being shown for too long.

Although most of us don’t ever think about screen burn-in anymore, it can still be a problem with OLED displays like the one used in the S8. Smartwatches with OLED screens can suffer from burn-in, too, because their displays are often left on at a high brightness with static elements showing (like parts of the watchface). That’s why Google’s Android Wear has a “display burn-in protection” setting for developers that shifts the display interface back and forth, although it’s not really a problem for regular users.

So, while the S8’s shuffling home button may seem odd, it’s doing its dance to protect your screen.