Mine does the same at the end slightly tappers off, but I then square it 90 degrees on my linisher and sand it flat. I also gave it a few extra mm for squaring it off Although the cut off saw isent accurate it's the easiest and cleanest cut I could get doing it at home as stainless is damn hard. Beats cutting it with a hack saw.
What you can maybe try BB with an off cut to see if it makes a difference is take the folding guard off, I know it's not safe but I notice that when the guard hits the work piece it tends to push the saw handle to one side. Maybe with out the guard the blade will run it's true coarse and not have the pressure of the guard steering it off coarse. I may give it a try next time I use it to see if it makes any difference, NormK idea will work to just use a brick or something solid with a flat surface as an end stop behind the open pipe end so you can push back against it as a jig then rotate the pipe around with the saw in the down position.
