As the feat is written, Ride-by-Attack only protects the rider from the movement related AoO. The mount is still subject to an AoO when it moves past the defender. However, in my campaign I have found that this facet of ride-by-attacks has made Mounted Combat actually useful. Without the use of ride-bys, mounts were rarely being targeted. Therefore, Mounted Combat was of almost no use.
- Kusuf