However the behaviour is too quirky/unobvious to make the approach usable.  My component when dragging does stuff between the touchstart and touchend events. [ I'm using "raw" event handlers as I had some problems getting the touch data otherwise].  

When the header is hidden and I drag everything is fine.  When the header is initially showing then I get problems.  A quick drag is OK (just touch drag release).  However if I  touch drag pause drag..  then during the pause (before the touchend) the bar appears, only to disappear when the drag restarts.  When I stop the touch I often get a "flicker" when the header appears, disappears and then appears again. 

This is even worse if I use pinch gestures on the iPhone.

Oddly enough there is no problem on Chrome using mouse events.

So, is this the intended behaviour or a bug?  My simple-minded view, in order to make things repeatedly understandable to users is that the header should disappear (perhaps) on touchstart but then only reappear on touchend.  Or just keep it there all the time would be fine.  

This appearing on pause and then flickering is not good however!