Sprite Editor doesn't remember changes after clicking somewhere on the Editor panel and then selecting image again, but button "Apply" is still active

2) How can we reproduce it using the example you attached

Not a regression (present in 4.3.x)
Reproduced in 5.0.a19 too
See attached video
1 Create new project (or use attached)
2 Import some image and make it "sprite" in Texture Importer
3 Set sprite mode to "Multiple" and open Sprite Editor
4 Create some sprite in Sprite Editor, but don't press Apply
5 Click somewhere on the Hierarchy and then select sprite again in Project view

Actual results: the created sprite has disappeared, but button "Apply" is still active - pressing it doing nothing