Your appeal to authority not withstanding, unless you've placed one of your eight sensors into a bottle of water, all you're measuring is air temperature. Of course the air temperature rises in the fridge when you open the door - the point is that the embodied energy of that air is a fraction of the total thermal capacity of the system. Again, of course the temperatures rise when you add 6 or 12 cans of warm beer - beer is water - you're adding a significant thermal mass that's bringing energy to the party.
Since you claim to be all setup, run this experiment: Fill your fridge with a normal amount of food. Drop one of your eight thermometers into a water bottle and close the door. (The other seven can continue to measure air temp.) Allow time to achieve equilibrium. Open the fridge, use a fan to force out all the air, close the fridge. I'll bet a six pack of your favorite brew against hard data that the temperature of the sensor in liquid doesn't change appreciably over a "normal" window of having the fridge open. You'll see a rapid climb in air temperature as that air is replaced, but the water will not move in a significant way in such a short window.
Finally, COLD is not a thing that escapes. HEAT is energy, which we know can't be created, only moved or transformed. In this case, the compressor uses the adiabatic process to move heat energy out of the system. It is fighting against the natural tendency for energy to seek equilibrium - in this case the heat of the environment is trying to equalize into the low-energy space that is the fridge box. Heat warms the outside of the fridge until the outside saturates to the same level of energy as the environment. The warm outside of the fridge warms the "middle" of the insulation, which then warms the inside, and so on. We can talk about conduction, convection, and radiation, but the gist of things is that heat outside is trying to move inside. This is the (a) I mentioned in my post above - heat energy conducts (mostly, a small amount radiates, and a little is convected) from outside to inside. The better the insulation, the slower this process - but it would take infinite insulation to prevent this entirely. The other thing I mentioned was (b) moving warm items in, which is exactly what you called out above.
Returning to my earlier point: The temperature of the air relative to the liquid is how you get things cold - convection of air within the box moves heat out of the food/beer/etc., but this is a pretty low-efficiency process. The air has to be significantly colder than the food before a lot of energy moves. Having the fridge door open will certainly prevent you from cooling your food (as that differential disappears temporarily), but exactly because air has such a low specific heat (the index of how much energy it takes to raise a given mass by 1°), the compressor can remove the newly added energy with relative ease.
Again, if you have a liter of air and a liter of water, both at room temperature, and you try to cool both down by some number of degrees, you literally have to remove three-THOUSAND times as much energy from the water as you do from the air.