Fade Handles jump times in Edit Page

Is there any reason the white 'fade handle' triangles on both film and audio jump from 0:23 to 1:00 when dragging on the timeline. For me, its been like this for previous versions back to 12.5, but have never bothered to query it. Anyone else experience this?

Because frame 24 is 1 second.

Ok thanks Jim, blindingly obvious once pointed out!