...Gromit is designed that way.
Bingo.
On a small display, Gromit eliminates things that don't work well when the screen real estate is limited, like page titles and thumbstrips. The page title is fighting for space with the navigation icons, so something has to give. Otherwise, the title ends up wrapping, and pushing everything else down. In fact, without some Javascript/CSS intervention, the navigation icons get scrambled.
It has nothing to do with iOS, or even with whether the device is a "mobile" - it's driven entirely by the window size. In a desktop browser, try shrinking the window, and you'll see the effect.
ETA: When I did this, I was thinking primarily of a title bar that would be showing the album or folder title, which is generally not all that important for the slide image. Losing the image-specific title is a little different. I'll consider changing the routine to move the text down, rather than hiding it. That's what the thumbnail page does. But that
will reduce the space available for displaying the image, so....