Editing : Edit Modes and Tools : Grid Mode : Grid Mode Lock

Grid Mode Lock
To ensure that you do not inadvertently change the Grid mode setting when using Edit mode keyboard shortcuts, you can enable Edit/Tool Mode Keyboard Lock.
To lock (or unlock) the selected Grid mode:
1 Click the Grid mode selector and choose Absolute or Relative.
2 Select (or deselect) Options > Edit/Tool Mode Keyboard Lock.