1) Go to Catalog -> Categories
2) Find any category and go to the rollup screen.
3) Add any child category rollup.
4) After adding child category rollup user is redirected to the newly added child category and displayed rollup of that category.
This is the case with all the operation Add/Update/Delete. User should remain on the rollup page of the category for which adding child category like when performing Add/Update/Delete with parent category rollup.