There's also this from the datasheet:
1. The use of parasite power is not recommended for temperatures above +100°C since the DS18B20 may not be
able to sustain communications due to the higher leakage currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the DS18B20 be powered by an external power supply."
Note the question said the temperature in the room is stable, it didn't say it necessarily under 100 degrees C. It also didn't say the room is in a residential home and not some factory or lab. If you hook the unit up using parasitic power, which it is built to function on only under 100 deg C, then you can get variations.
2. There is also a variation for the device as well: