Sonja,
I think the version of your evaluation edition was in Beta (3.0.x). We did some enhancements on the CurrentExtent stuff since 3.1.x so it will have some differences from then. In the previous version, we used CurrentExtent to synchronize the client’s and server’s position, it works fine for the first time but after several postbacks, it will always lose some accuracy because of the limits from javascript. That’s why we are using the center point and scale to synchronize current viewport position now, which will not lose any accuracy but yes, it will change a bit your current extent written with the previous version.
So I think you need to change a bit on the current extent to make it fits the new release. Sorry for the inconvenience and please let me know if you have any issues.
Thanks,
Ben