GLUT display window stretching out of window box and duplicating pixels

I've created a simple GLUT program that should simply draw a triangle:

#include <GL/glut.h>
#include <iostream>

using namespace std;

void render(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glBegin(GL_TRIANGLES);
        glVertex3f(-0.5,-0.5,0.0);
        glVertex3f(0.5,0.0,0.0);
        glVertex3f(0.0,0.5,0.0);
    glEnd();
    cout << "ran" << endl;
    glutSwapBuffers();
}

void update(int value) {
    static_cast<void>(value);
    glutPostRedisplay();
    glutTimerFunc(16, update, 0);
}

int main(int argc, char **argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(1000, 1000);
    glutCreateWindow("window");
    glutDisplayFunc(render);
    glutTimerFunc(25, update, 0);
    glutMainLoop();
    return 1;
}

...but it has unexpected results:

When I don't have the update function, it seems to only show the weird screen once and then it fixes itself. It also shows the correct display when dragging the window around. I think it may be an issue with my machine? I've been able to use OpenGL and GLUT before in the past.

I had this exact issue, same visuals, same environment. I feel silly for not trying earlier, but wsl --update and then a restart fixed this for me.