Windows 10, i7 4770, Asus GTX 1060.
Broken: 2.78.5 hash 72c9141
Worked: I believe in 2.78 did work.
Short description of error
When an object is parented you cant get motion paths from it. It just wont calculate them.
Exact steps for others to reproduce the error
open a new file,
create 2 objects,
parent one to the other,
animate the parent,
go on the properties panel of the child > go motion paths, set your settings, and voilá no motion paths.