Ruler zero position reset but positive/neg reversed

Hi all -

I am trying to reset the position of zero but it doesn't seem to be working properly (yes, artboard rulers are selected). When I drag from the upper left corner to set zero at a new position it works and the 'physical' rulers that you see to the left and above are reset so the zero is showing where I would like it to be.

So now, anything above 0 (or to the right of 0) should show a positive number in the coordinates boxes. But no....

Instead, it shows a *negative* number. So what should be and what looks to be on the actual artboard when I look at the rulers position at, say, 500px, in the coordinates box it shows at -500px.

Does anyone know what gives?