Yes, it does make the difference when you move TAB ON DIAPHRAGM-METERING RING manualy (in the blue circle) - checked now once more - needle moves as it should, confirmed. There are no pins/sensors for the check if the lens is on the body - there is no reason why it should not works without the lens off the body.
By using a lens on the camera and then adjusting the aperture ring, you are letting more or less light onto the meter. Having last used one decades ago now, I am not sure how it all works but without a lens on the camera you are letting in much more light than necessary and think, when would you take a picture with the lens not on the camera anyway? So there is no need for the meter to work WITHOUT a lens on, which you have found out, do I can only think that this is all part of how the camera was made.
The bit of text that I found on a search says what I mean = 'The light meter uses two CdS cells and is fully coupled to the aperture.' ie as said above, the meter won't work without a lens on the camera.
Also, from what I've read, the cameras are quite old now and a lot of people recommend getting an EXTERNAL / handheld meter, from which you transfer the readings across to the camera, especially with anything other than print film, which has a larger latitude in exposure terms when compared to slide film say.
I hope this helps,
Terry S