Bit of a glitch to fix :

I used the Change Reservation function to add some text to the "Other Requests" box. As soon as I saved this update, I received the "We noticed an update to the stay preferences on your SPGŪ profile" email.

It seems this was triggered by the "Save these for my next booking" option, which is on the reservation preferences and checked by default. This hasn't been programmed to understand that updating only the "Other Requests" field on the reservation, without changing anything else, isn't a profile update.