Issue using object space normals in shader graph

[delicate furnace]

I made this simple shader graph to test this issue, made a material, and applied it to a cube. It looks as expected with no rotation, but when I rotate the cube around the Y-axis, this strange effect happens

before: the side on the right is all black

after rotating a little

It's using object space normals, so why is it rendering differently? shouldn't the normals stay the same when rotating? since they're in object space and not world space

perhaps it's a precision issue? i added a Round node and now it seems to work as expected