Had another weird one today.
Driving east on the M5 with TACC set to 110km/h. (Not that I wanted to go at that speed but I find I don't get left behind if someone goes a little over 105km/h. The traffic in front was doing 90-95km/h and I was staying 7 clicks behind. All of a sudden I started to slow. It wasn't phantom braking but more just easing off on the accelerator. I checked the display and TACC was now set at 80km/h. I had touched nothing and had not gone past any speed limit signs (which it is supposed to ignore on motorways). And why 80? I have my default TACC to +5.