why can't the contents of stencil buffer be replaced - opengl

Question

I draw two triangles. Before draw the first, I set the contents of the stencil buffer to make sure the stencil test will fail. So the first triangle won't be rendered on the screen. At the same time, I call the func "glStencilOp(GL_REPLACE, GL_KEEP, GL_KEEP)" to replace the contents of the stencil buffer with new value ref. Then I draw the second triangle. Theoreticaly, the stencil test in drawing this triangle should pass and the second triangle should be rendered on the screen. While in fact, the second stencil test failed again! I can't find the reason. Can anyone help me ? Thanks.
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glStencilOp(GL_REPLACE, GL_KEEP, GL_KEEP); // replace stencil buffer when test failed
glStencilMask(10); // set mask 10
glClearStencil(13); // set clear value 13
// since mask is 10 and value is 13, so the contents of stencil buffer is 8
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glStencilMask(0xff); // enable the writing of stencil buffer
glStencilFunc(GL_EQUAL, 9, 0xf); // (0xf & 8) != (0xf & 9)，stencil test failed
// this triangle won't rendered
glUseProgram(shaderProgramOrange);
glBindVertexArray(VAOs[0]);
glDrawArrays(GL_TRIANGLES, 0, 3);
glStencilFunc(GL_EQUAL, 9, 0xf); // now ref is 9，theoreticaly, the stencil test should pass
// in fact, the test still failed! I didn't know why.
// this triangle should have been rendered
glUseProgram(shaderProgramYellow);
glBindVertexArray(VAOs[1]);
glDrawArrays(GL_TRIANGLES, 0, 3);
glBindVertexArray(0);
// Swap the screen buffers
glfwSwapBuffers(window);
glStencilMask(0xff);
glClearStencil(0);
glClear(GL_STENCIL_BUFFER_BIT);