Continuous heat called when set to 21.3c

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Why does the tado thermostat keeps calling for more heat when ever temperature is set between 21.1and 21.4.
So for example if the temp is set to 21.3 or 21.4, it’s still calling for more heat until it reaches 21.6.
Should it not stop until the temperature is below 21.4?
I dont have this problem when it’s set to 21c or 21.5c for example.

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