The deformation menu ALWAYS works in relation to the Tool>Modifiers>Preview window’s XYZ coordinates. These coordinates never change, regardless of how the model is rotated within the window.
This actually gives tremendous control over your deformations, just as soon as you understand that principle. In fact, it frees you up from having to remember what the object’s XYZ coordinates are – simply rotate the object so that it sits a certain way in the window, and then apply your deformation.
If you want to keep the object’s XYZ coordinates aligned with the preview window, you can start a rotation and then hold down the Shift key when you get close to the orientation you want. The object will then snap so that it’s squared off at 90 degree angles with the preview window.
You can also Store the current orientation, and Restore to it at any point after that. (The default Restore is to the starting orientation.).
I don’t know what the deal is with the way the deformation behaves along the Y axis, but can probably find out for you.