OpenGL random texture data when using multiple threads

I made an opengl app recently that uses another thread to load the images while the other thread is rendering. Everything works great except at the startup. After the second thread is created and sets up opengl I return to the first thread and call wglShareLists to share contexts. At that point random opengl data shows on the entire screen until I start rendering. Keep in mind. All of this happens BEFORE my windows is even visible on the screen.

Why does this happen? Can it be stopped?