problem with glBlendFunc (GL_SRC_ALPHA_SATURATE, GL_ONE)

OpenGL OpenGL: Basic Coding
1

glBlendFunc (GL_SRC_ALPHA_SATURATE, GL_ONE)
(need for glEnable (GL_POLYGON_SMOOTH))
not working with DOUBLEBUFFER
why?
example in MSSDK is working with SINGLEBUFFER only!