The thermostat item is the “Setpoint (heating)” channel and the Temperature item is the “Sensor (temperature)” channel.
It seems to report the current temperature correctly, but when I click the up or down buttons on the setpoint control I get that message. Although the log claims that the setpoint was changed nothing happens in the actual thermostat.
It’s caused by the framework sending QuantityType commands to the binding, but the binding does not support these command types - there’s not a lot that can be done to change this and if it’s a major issue I would suggest to use the development binding which has support for UoM.