Try removing the conditional on "applied"

It shouldnt be too bad to keep running that code if its only every time the mouse enters the chart rather than over it. You are having a timing issue were the

MakeAllTextBlocksNonHittable

function is being run before the data is actually rendered to the chart. So one solution is to change:

private void DoughnutChart_MouseEnter(object sender, MouseEventArgs e)

        {

            if (!applied)

            {

                MakeAllTextBlocksNonHittable(sender as FrameworkElement);

                applied = true;

            }

        }

to:

private void DoughnutChart_MouseEnter(object sender, MouseEventArgs e)

        {

                MakeAllTextBlocksNonHittable(sender as FrameworkElement);

        }

-Graham