I was testing a new build (ShadarKai, Rogue 6, Ranger 2, Bard 12) with throwing weapons in the dojo and found that, when I turned on improved precise shot, Return to Sender went through all targets with no effect and stuck in the wall behind the kobolds. I went out to Searing Heights and got the same results. Even with just one target, IPS sent RtS straight through it to end up in the wall or ground behind with no effect. I bought a bow, arrows, shuriken, daggers, and axes in Hammer and Chain and found that, while all worked as intended, throwing axes and RtS had no effect on any target while in IPS. All weapons worked fine with just precise shot/archer's focus.