System Information
Operating system: Windows 10
Graphics cards: Intel(R) UHD Graphics 630, NVIDIA GeForce GTX 1060

Blender Version
Broken: be060c3990ad from 2019-06-29 20:58

Problem:
If I use an Empty as Pivot Point for a Simple Deform Modifier (Bending Mode) and a Lattice with w-dimension set to 1,
only setting the bending to Empty's local z-axis has an effect.
If I want the x-axis or the y-axis of my Empty to have a bending effect, the w-dimension of the Lattice has to be set to a value higher than 1.

But now comes the surprise to me:
With the w-dimension of the Lattice set to 1 and the bending axis set to the local z-axis of the Empty,
I rotate the Empty 90 degrees around the gloabal x-axis so that the Empty's local z-axis is now aligned with the global y-axis
and my Lattice is bended around the global y-axis.
Why can't I have the same effect by chosing the Empty as Pivot Point for the bending in the Simple Deform Modifier and setting the bending axis to the Empty's local y-axis?

Unfortunately, the Blender 2.8 Manual only explains "Axis, Origin" as the setting of the Pivot Point Object for the bending, but not the axis setting of this Pivot Point Object:
https://docs.blender.org/manual/en/2.80/modeling/modifiers/deform/simple_deform.html#bpy-types-simpledeformmodifier