For another perspective that probably doesn’t apply in your situation since the behaviour changed after an update. But for those curious:
“the odds of me getting a stable temperature of exactly 73.4 are pretty low”
Except that thermostats lie. Especially Honeywell ones.
They’ll undershoot by a degree and then overshoot by a degree during their heating cycle 3x~ per hour. Your reading of 73.4 (23C) may be reporting as very consistent although in reality it’s all over the place. This is by design.
If you change the setpoint, often the thermostat’s “reading” will instantly change to read the same as the setpoint as long as it’s within a degree or two.
Not to mention, thermostats are often placed next to return ducts so that they’ll get a half decent reading since they’re not in motionless air, but this only goes so far. Often the reading can be consistently higher or lower by a couple degrees depending on placement and air dynamics. If you do 24/7 circulation this can even-out heat inconsistencies due to windows, motionless air and such, but can be not worth the cost (and don’t even think of circulating a lot if you have an old PSC motor, only if you have a modern ECM motor which have better lifetime and efficiency)