Why does xinput not have an effect on my mouse in XFCE?

I'm trying to fine-tune my mouse acceleration settings. The XFCE "Mouse and Touchpad" dialog is confusing and seems unable to get precisely what I want. However, when I use xinput to tweak my mouse, the settings don't seem to have any effect. I tried changing "Device Accel Profile", "Device Accel Constant Deceleration", and "Device Accel Velocity Scaling" to a variety of values and none of them seemed to have any effect, even though xinput list-props does show the settings I want.

I'm using a Logitech G5 on Xubuntu 16.04.