The shelve feature should let me select what I want to shelve and it should allow me to shelve new files that aren't scheduled for inclusion yet.
More importantly, when addressing an existing shelve, that shelve shouldn't get overwritten with the new changes, but rather amended.

Scenario: I had one changed file and three new files. I pressed shelve and gave it a name. Suprisingly, only the changed file was shelved. Then I added the three new files and shelved again using the same name. Guess what, the shelve was overwritten and my changes to the existing file were lost.