Is this the expected behavior?
1. Create an empty org file
2. Insert
* Test
* Test 2
3. With the cursor at Test, hit C-x n s to narrow the view to the Test subtree
4. Hit C-c C-s to schedule the line at any date.
As a result, the SCHEDULED keyword is _not_ included in the narrow view, and inserting things after the Test heading moves the SCHEDULED keyword away from its second-line position.
Cheers,
Michaël