I finally remembered to come ask the question here: on my 5DsR, with the camera set to shoot RAW and ISO 100, I see in the viewfinder a buffer size of 12 shots. Whenever I take even just one shot, I instantly see the buffer drop to 9 then climb its way back to 12. Anyone else see this with their 5Ds/5DsR, and perhaps know why it's doing that?