While in “Object mode”, the “Plane” handle (the tiny grid icon) of Gumball aligns to a single control point relative to its highlighted control polygon. In the case of selecting one of the 4 corner control points of a circle, the “Plane” handle is displayed rotated exactly 45 degrees relative to the square control polygon.
This is a great opportunity to be able to move the control point diagonally along the local “Plane” handle. It’s natural to do so by holding the Shift key to lock the dragging of the “Plane” handle from free movement to ortho movement along its local grid (not along the CPlane grid). If “Grid snap” is active, holding Shift while dragging the “Plane” handle also should respect this option and snap to every unit along the local grid (not the CPlane grid).
However, when I hold Shift and try this on a corner control point of a basic circle, the dragging of the “Plane” handle is not locked to its local icon’s orhto directions (I mean the current local coordinate of the rotated “Plane” handle). Instead, a new bug occurs when I hold Shift and release the LMB. The yellow selection colour is added as a duplicate to the black circle and remains this way even if I select other control points or other objects. To turn off the yellow selection duplicate, I’m forced either to hide the control points of the circle, or drag the control point and press the RMB while the LMB is still held (that cancels the dragging).
There is also a 2nd bug related to the Shift key being used while dragging a point object (not control point). Currently, the “Plane” handle can snap to the CPlane grid only when the “Grid snap” is enabled. However, when I want to override that by dragging the point and then holding the Shift key (the modifier key typically used to temporarily switch the Ortho), the Gumball disappears and cancels the dragging. In Rhino 7, the Gumball does not disappear, and the dragging of a point is not cancelled under the same circumstances.
I’m aware that in Rhino 9 holding the Shift key before or after holding the LMB on the “Plane” handle switches the mode from moving to scaling. However, I have a proposal to do so only when the Shift key is held preliminary (before pressing and holding the LMB on the “Plane” icon). That will leave the opportunity to initiate a dragging by the “Plane” handle, then hold the Shift key to enable local ortho along the current orientation of the “Plane” handle’s icon.