I also cann't see any difference.
Works both the same for me.
This vid I hope this is more clear than my first one
OK 12Gage, I see what you mean now.
The difference is in Assembly but not in Part (where distances are always + on the cursor side)
I can only explain it that for co-ordinate system planes in an assembly the + direction is along the 'other' axis, but for the base reference planes it is along the surface normal.