Variable not accepting value [on hold]

I have a Boolean control_refresh in class A and in a class that inheres A i have a function in which is control_refresh=true;. The code compiles fine.

file_1.cs

public partial class graficki_editor : Form
{
    ...
    internal bool control_refresh = false;
    ...
}

file_3.cs

public partial class graficki_editor : Form
{
    ...
    private void canvas_paint(object sender, PaintEventArgs e)
    {
        debug_label.Text = control_refresh.ToString();
    }
    ...
}

file_2.cs

internal class projekt : graficki_editor
{
    ...
    private void sloj_Checked(object sender, EventArgs e)
    {
        if (((CheckBox)sender).Checked)
                objekti.ElementAt(pan.Controls.IndexOf(((CheckBox)sender).Parent)).visible = true;
        else objekti.ElementAt(pan.Controls.IndexOf(((CheckBox)sender).Parent)).visible = false;

        control_refresh = true;
        canvas.Refresh();
    }
    ....
}

(Non relevant code is excluded)

In the scope of sloj_Checked I can set control_refresh and in than scope it works fine. But when the control is refreshed and paint event is called the variable stays the same.

My question is how do I change the variable?