Keying the Spawned Property of a Spawnable Breaks in the details panel

The spawnable mesh seems to be breaking when their spawned property is altered. If you uncheck the spawned property in Sequencer, the Details panel also breaks similar to keying the property.

This is a Regression from 4.15.3

1. Open a project
2. Create a new Level Sequence
3. Open the Level Sequence
4. Drag a Cube into the Level Sequence to create a spawned mesh
5. Press the Spawned Track Add Key Frame button

Result: The mesh's details panel breaks and the mesh is unselected in the viewport

Expected Result: The details panel doesn't break and the mesh is still selected in the viewport