Save now appears after moving blocks, saving, switching sprites, and back to original

[kchadha]

Steps to Reproduce

1. Move blocks the workspace of sprite 1.
2. Save now should appear, click "save now"
3. Switch to another sprite
4. Switch back to sprite 1
5. Observe that "save now" appears again <-- It shouldn't.

After step 5, if you click save now, and switch between sprite 1 and the other sprite, save now does not appear again.

Possibly what's ultimately causing #4603 or perhaps just another specialization of that issue.