This is the same as with the iPhone.
On these devices you do not scroll using the scroll bar, instead use two fingers side by side to scroll the portals
Hope this helps.
Thanks; that worked. Not particularly intuitive but gets the job done.
Took me a while to realise it too, so now I put a small message below the portal giving instructions..
since my interface is (at the moment) purely for iPhone / iPad it makes sense, but would be out of place in a browser.