The reason is that when you were in the previous week, prior to making roster changes you had advanced to the following week, which carries the information as it stood from the prior week. Then you had returned back to the prior week and made changes. When advancing to the next week, the data for that week was already there, so it shows the information prior to the changes.
To resolved, return back to the last week in the league that contains scores. Select Utilities > Delete Future Weeks Data. The data for weeks after the week you are presently at will be removed. Now, when advancing to the next week, the rosters, as they appear now, will be carried over to the following week.