This happens because you've explicitly specified that StepType="Start" for your last step, remove this line of code from Issue6 and it will no longer display the Next button.However, when you do this you will notice that the last step will now display two buttons:
1) Previous
2) Finish
This is by design as the Wizard control's purpose is to collect data from user by separating it into logical chunks, making data collection more intuitive and submiting the data to the server for processing at the last step.If you only want to display a previous button on the last step I would suggest using a MultiView control