It's ~24 hours later and the set point is still at 18.1C. So I have no idea what's going on. It's actually stranger than that. At least according to the graph the setpoint has been changing a tiny bit, but it's going up and then down again. It varies between 18.0X and 18.1X, which you can see in the graph as jagged bits:
I could just been precision errors on the graph, but I wouldn't expect to see it go down and then back up again, rather I'd expect flat spots that continued to step up.