I am not 100% certain, as I have no steelhead old enough to test. However, I do remember that using PBR, only the lowest in-path interface number (in-path0_0) would optimize, unless you issue the hidden command "in-path oop all-ports enable". In which case it would allow other in-paths as well. I have gone back as far as I can in my lab (8.6) and the command is no longer there, hidden or otherwise. I can only summit that no all ports are enabled for PBR regardless.
As I said, I am not 100% sure, without testing it, but it may be a steer for you.
Can I ask if there is a problem with it, or just an observation of the new behavior?