C# drawing a line weird bug

Okay I have this code after a button click:

Code:

            System.Drawing.Pen mypen;
            mypen = new System.Drawing.Pen(System.Drawing.Color.Red);
            System.Drawing.Graphics gf = this.picMap.CreateGraphics();
            gf.DrawLine(mypen, 0, 15, 100, 15);

The horizontal line is drawn over a picturebox and I see it fine.
*Note I have this image in a panel and the image has horzontal and vertical scrolls and when I click it to move it down the line drawn over the image disapears. (it shouldnt disappear untill it has moved out of view)

In another example, I made a project with the exact same code to test this and the line drawn the same, I click down and the line is still there. I no that I have to have the draw image in the Paint event but it wasnt working in it and thats why I simplified it to try and find the error.

When it was drawn in the Paint event it would disapear when I click down on the scroll button, but if I click down or up fast enough you can see it flicker. I almost simply copyed and pasted my code as I was updating my project. Code wise this is the exact same code but would there be some sort of setting that would effect this...

 

Solved used the PaintEventArgs e.Graphics instead of creating a new Graphics via CreateGraphic. Although I am unsure why the CreateGraphics didnt work in my application because I tested the same code in a different one project using the same controls and it worked...