This is kind of a windows thing that I just ran across today.
Depending on where you last clicked on a property manager dialog box hitting the space bar has different, but useful, effects.
Last clicked in text box (such as entering a dimension.) Hitting the space bar will add a space. Nothing new here.
Last clicked in a check box as in creating a reference plane by distance and clicking in the reverse plane check box. Hitting the space bar will toggle the checkmark, i.e., move the plane from side to side of the starting plane.
Last clicked in a rollup box in property manager. Hitting the spacebar will cause the box to rollup or expand.
Last clicked on an icon on the left side of the property manager, i.e., the distance plane icon in reference plane PM. Hitting the spacebar will toggle the icon off then on then clear the text.
In a PM which has multiple rollup boxes the behaviour of the spacebar is inconsistent except for checkboxes.