GLFW magenta color causes unexpected behavior

When I create a window with GLFW (on a Windows operating system) and set GLFW_TRANSPARENT_FRAMEBUFFER to 1 via glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, 1); I can't draw a rect with a magenta color glColor3f(1.f, 0.f, 1.f);. This color causes the rect to be transparent and makes me able to click through this part of the window.

I did not expect this behavior and also did not find any documentation that explains this.

I used the example code on the GLFW homepage and added a gray, yellow and magenta rect of which only the gray and yellow rect produce expected behavior.

Screenshot that shows the window

#include <GLFW/glfw3.h>

int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    // ADDED THIS LINE
    glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, 1);

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        // ADDED THE FOLLOWING LINES
        // background
        glColor3f(0.1f, 0.1f, 0.1f); // gray
        glRectf(-0.75f, 0.75f, 0.75f, -0.75f);

        // unexpected behavior: makes part of the window transparent and click through
        glColor3f(1.f, 0.f, 1.f); // magenta
        glRectf(-0.1f, -0.1f, 0, 0);

        // draws yellow rect
        glColor3f(1.0f, 1.f, 0.f); // yellow
        glRectf(-0.1f, 0.1f, 0, 0);


        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

The magenta color gets drawn correctly when GLFW_TRANSPARENT_FRAMEBUFFER is set to 0.