The code you have posted seems to be correct. From what I see on the screenshots, a page size set to 100 should me more than enough for the portrait mode (which seems to contain about 14 items).
A couple of things come to mind - please verify that the items do not resize themselves after they are being displayed (due to images without width and height being loaded). In virtual mode, the listview items are re-positioned manually, and such behavior would break that (something similar to what your screenshot shows). Also, please verify that the service endpoint functions correctly and returns correct amount of data items, while respecting the paging parameters provided.
Last, but not least – I re-tested our endless scrolling demo on an iPad (iOS 6), and it works as expected. You may also consider using this functional example as a starting point for your current implementation.
In case you need any further help, please let us know.
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