I have seen much of these problems with Scrum, as well. Redefining "complete" so we can book the points, but actually finish it in the next sprint is very, very common. Finishing early, starting on a future story, but the scrum master asking you to not bring that story into the current sprint, in case you don't finish it, is also a frequent occurrence. My view is "if I don't finish it, it rolls over, so who cares", but this is frowned upon since it throws off the reports.