USplineComponent::GetInputKeyAtDistanceAlongSpline() returns time (based on the spline's duration) at the distance rather than the input key. This method should be deprecated since current implementations using it may be expecting the current behavior. Two new methods should be added - one to return input key, the other to return time based on distance along spline.
This method was added in CL 2089561 in 2014 so it is a longstanding bug.
TBD (will enter soon)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-141098 in the post.