If so, he should have benched it level so that wouldn't happen. That's the whole point of the machine in the first place. Anytime you aren't level you can't dig level, and are making the machine work far harder trying to fight gravity with the slewing bearing. They will operate on about any slope, but you are just tearing up shit for no reason. Whenever you are operating equipment, of any kind, you need to prepare the working surface.
You see the guys that really know what they're doing, they will actually climb up and intentionally work on top of the spoil pile when they're loading certain trucks, feeding rock crushers, setting equipment and pipe, etc. so that they are sitting up high enough to see better and have better and higher reach. If you are trying to grade, the first thing you ever do is find or make a level pad to work on, so everything you do is level too. With the dozer blade, you also need to be using that as a stabilizer when doing almost anything.
Just noticed b's post, i was talking about earlier about it tipping on a slope. A road is different, because you can't change it.