In Version 8.0, when opening a bookmark that utilizes the same data source as the rest of the workbook, we would be prompted with a "Data Source Name Conflict" message:
In Version 8.1, Tableau automatically will add a new data connection with a number added to it--in the screenshot above, a Data Source called "Student Gradebook Detail by week Last Page (Course & Teacher) 2" will result in my data window.
Please bring this helpful message/dialog back to Tableau. It makes no sense to create an additional data source for a workbook that is already using the data source referenced in the Bookmark. Yes, I can replace the data source after it is added, but it causes more work for the Tableau developer, and it just doesn't "FLOW" or make much sense to me at all.
NOTE: This same functionality should exist for Copied/Pasted Sheets in version 8.1