Steps to reproduce:

1. Open attached project
2. Open scene "MultiSelectRotation"
3. In hierarchy, select Cube and open animation window
4. Inspect Interpolation properties set to both of the object
5. Multi-select both properties in Animation window
6. Right-click on one of them and set interpolation to Euler
7. Inspect both cubes again ant notice that Interpolation was changed only on the one that was clicked

Expected result: both object have their Interpolation changed

Note: Same happens if selecting "Remove property", but this can be worked around by pressing "Delete" on keyboard.

Reproduced with: 5.1.4f1, 5.2.4p1, 5.3.2p3, 5.4.0b6