There is a screen flicker issue with the picker example after selecting the rank field. This could probably be any field though with a drop-down.
The issue is also visible in the Safari 5.0 / Chrome Browser
If you select the Rank field using the web browser (NOT ON THE ACTUAL DEVICE) the drop-down box appears in random locations (see attached screen shot), which I assume is caused by the fact that the sub-menu is created on the actual iPhone now after selecting the rank field.
If you select the rank field on the iPhone and choose a selection and choose done, then when scrolling up /down on the iPhone it appears it's still wanting to redraw the sub-menu from when the Rank field was selected.