Problem when drawing directly on the Device Context in Windows 7

On some computers running windows 7, if you draw using DC.LineTo(x,y) directly on the screen device context, your drawing might not show. Possible solutions are:

- The quickest workaround we have found yet is to draw a small circle also, because for some reason drawing a circle forces a screen repaint, so a simple extra line like DC.Ellipse(x,y,x+1,y+1) can solve the problem

- If you switch the windows theme to Windows Classic, everything will work fine.

Strange bug!