OnPaint function causes artifacts to show up in a New Editor window

If the the onpaint function is used it can cause the top and left sides of the screen to retain artifacts. Attached image for reference.

1. Open the Editor
2. Create a new widget blueprint
3. Create an override for the OnPaint function
4. Create the blueprint in the attached image
5. Compile and save
6. Open the level blueprint
7. Add the widget to the viewport
   Begin play > Create Widget > Add to view port
8. Play in a New Editor Widow (Note: this is important )
9. Notice that the top and left sides of the screen retain artifacts as the camera is moved around

Expected: The function should draw a line on screen
Result: The function draws a line on screen but also causes the top and left sides of the screen to have a hall of mirrors effect