Alt-G only works on occasion, and then, not really…

It seems quite random when blender resets a position using Alt-G. Often Alt-G does nothing.  When it works the viewport shows a reset ball but the graph editor shows a key being inserted at the same y-value as the previous key. If i then scrub the timeline the Viewport undoes the reset too, to fall in line with the graph editor. I get a key, but the position is the same as the previous key. Halp…