With the linux-hwe kernel (4.8.0-37.39~16.04.1, xenial) from the "kernel PPA", my two USB3 drive are successfully ejected and they stay poweroff.
With the linux-hwe kernel (4.8.0- 37.39~16. 04.1, xenial) from the "kernel PPA", my two USB3 drive are successfully ejected and they stay poweroff.