There is a small bug in SifterReader v1.5, but it does not effect the functionality. If you use the "prev" or "next" buttons to navigate your issues and try to view a page before the first or after the last, you'll get a special page that says, "Oops!" and the error is "JSONException: No Value for Page." Just press the back key for now, and it will take you to the last page you were on.
I apologize for the inconvenience. I will try to fix this as soon as possible. I have already entered it into the bug tracker as issue #25 Next and Previous buttons not stopping at first/last.