Why does analog video signal in computers change?
The issue with the old fashioned analog video signals like your "d-sub" connector (SVGA probably) carries is that there was no guaranteed exact registration of where the pixles are to the sync pulse.  In analog this didn't matter.  The image would appear a little left or right, and you'd expect to adjust the monitor for that anyway.

Most modern screens display discrete pixels at fixed locations, so the electronics needs to know exactly what part of the analog signal represents which pixel.  This is no problem with a proper digital video feed since each pixel is defined explicitly.  When the monitor is given a analog signal, it needs to get the timing of the A/D just right to sample the intended pixels.  Things would look blurry if it sampled between pixels so as to get the average of two adjacent pixels instead of individual pixels.

The auto adjust is usually the monitor inspecting the analog stream and inferring the true start and end timing of the picture information.  Since this is digitally generated on the video card, it won't change as long as the card isn't reconfigured, but can be different from card to card.

I am surprised that opening the window changes anything.  Perhaps the timing in the monitor is susceptible to temperature changes, but these would happen over a bit of time, not instantly when you open the window.  Perhaps the different lighting makes you see things differently.  I don't have a good answer as this symptom makes little sense.