There are many types of keyframes for which you can't jump in the timeline to the next or previous keyframe, such as:
Blend shapes
Ramp texture's selected position
Mash strength
It doesn't work with either the buttons or the arrow hotkeys. I posted about this a few days ago only with regard to Mash animations, but it's a more generalized problem. It really slows down the workflow in dealing with editing these types of fcurves.