Why is glewIsSupported() wrong?

[Lindley]

I have the following code:

    GLenum err = glewInit();
    cerr << glGetString(GL_EXTENSIONS) << "\n";
    if (err != GLEW_OK ||
        !glewIsSupported("GL_ARB_color_buffer_float GL_EXT_framebuffer_object GL_EXT_packed_depth_stencil"))
        capable = false;

The printout of the extensions clearly indicates that all three of those extensions are present, yet the glewIsSupported() call is returning false. If I break it down to three separate checks, the first two work but GL_EXT_packed_depth_stencil does not register as present (despite being in the GL_EXTENSIONS printout).

What could possibly be causing this?