Reproduction steps:
1. Open user's provided project "21_2_SS_Test.zip"
2. From the Assets folder drag "Sprite Shape Profile.asset" into the Scene
3. Click on "SpriteShape" in the Scene, select "Edit Spline" in the Inspector
4. Click on a control point and verify B, N, M (default) shortcut keys
5. Select "Sprite Shape Profile.asset" in the Assets folder
6. In the Inspector, add/remove sprite in sprite variant list
7. Click on SpriteShape in the Scene, select Edit Spline in the Inspector
8. Click on a control point and verify B, N, M (default) shortcut keys

Expected results: After editing the sprite variant list in SpriteShape Controller, shortcut keys work
Actual results: After editing the sprite variant list in SpriteShape Controller, shortcut keys do not work

Reproduced in: 2021.2.0a13, 2021.2.0b12, 2022.1.0a10
Not Reproduced in: 2019.4.30f1, 2020.3.18f1, 2021.1.21f1, 2021.2.0a12