How to reproduce:
1. Open the attached project named "Case_1110525"
2. Select the "First_Sprite" sprite and open the Sprite Editor
3. Click Slice (Use either "Automatic" or user-defined settings)
4. After slicing the sprite select the "Second_Sprite"
5. When asked to apply pending changes click Apply
6. Select the "First_Sprite" again

Expected result: First_Sprite is sliced
Actual result: First_Sprite is not sliced

Reproducible with - 2017.4.19f1, 2018.3.3f1, 2019.1.0b1, 2019.2.0a3

Workaround: User must re-slice the sprite and click the "Apply" button inside the Sprite Editor window

Notes:
After trying to slice the sprite Sprite Editor will show that the sprite is sliced even though there is no drop-down menu to select individual sprites