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
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
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-45195 in the post.