when i am in a Shaded Viewport, and run the non permanent
_Shade command, there are various options to Show the grid, axes, curves, isocurves etc. The option to show/hide curves does not work here, it toggles the Z-Axis instead which has been a bug since early V5 days.
To repeat, run
_Shade and set it to
_DrawCurves=Yes. Press Enter to exit the non permanent
_Shade display. Create some curves in the document. Then Run
_Shade and set
_DrawCurves=No. In my case, the curves stay visible but a Z-Axis is shown. Once i use
_Enter and run
_Shade again, the curves are hidden as they should. If i set
_DrawCurves=Yes the Z-Axis gets hidden.
I do not understand why there is a Z-Axis involved at all. The viewport was in permanent Shaded Display mode and when i enabled
_Shade which it is set to