That sounds awfully much like the 'thin' bit of the keyhole slot C has been broken off & your description of how it hangs off the side of the Spyder is pretty much
EXACTLY what a mirror with a broken upper pellet does - it is likely that your upper pellet on that side is broken & needs to be replaced. I've had a quick look but can't readily find my pics of broken vs complete pellets, but I'm reasonably sure that if you could remove the two little screws holding it in & then take & post up a pic of the elements of that upper pellet, someone here could definitely identify it as broken or not - or you doing a 5 second comparison with the one you have that doesn't hang off like that could do the same, altho I do appreciate your concerns about removing something that can be so hard to get back on... :shocked:
The 'thin slot' is meant to have a section in it which is only just as wide as the shank of the pin behind the bulbous head; the thicker sections above & behind that (deeper into the pellet) are there to stop the head going in too far or down too far.... The thin bit is usually the bit that breaks, generally losing about a third of the 'side' of the slot, but that is the essential third & without it there, the head of the pin has nothing behind it to hold the mirror on, & there is not enough of the rest of the thin keyhole bit left to keep it in place, so the mirror flops out at the top instead of being held firmly in.

pps:
I really think you need a new upper left mirror pellet - sorry.