Just look at this accepted submission from this guy on youtube 196672015.

As you can see it has passed system tests. Now just submit ir again and it gives wa test 2. Which is coorect as for the case

1 2 0 0 1 1

It gives 0 but answer should be 1. He and probably many others are getting free rating points due to such errors.

We need fair evaluation Mike Mirzayanov