title: Why does unbinding a texture from a FBO clear the texture?
body: <p>I'm having some trouble with a render-to-texture operation.  I create a FBO, attach a texture, render to it, and everything's fine, but when I try to change the attached texture, either to 0 or to a new handle, by calling <code>glFramebufferTexture2DEXT</code> again, the texture I had attached becomes blank (all pixel values reset to (0, 0, 0, 0)).</p>
  
  <p><a href="http://www.opengl.org/sdk/docs/man4/xhtml/glFramebufferTexture.xml" rel="nofollow">The documentation</a> doesn't say that this is supposed to happen, and it's a bit troublesome for me because I need to retain the information in this texture.  Does anyone know why this is happening, and how to prevent or work around it?</p>