You can refer to figure 11 in the datasheet for default as non-latching mode with status register change plotter.
So when data is stored into data register, the status is going to high. then the read of data register done, the status bit will be clear to 0. then next new data stored in register, the status bit will change to 1 again.
So you need to read the status bit first to make sure it is 1 which means you have new data stored in the data register, then you read the data register. In this case, you should not get default value from data register any more.
Hint: the data measurement always take some time. after you change the power mode of sensor, you need to wait certain time to get measurement done and new data stored in data register. this time is different based on different over sampling settings.
At the same time, the normal mode is running in internal logic. during normal mode, the bus communicate have no lilmitation. you can always do read / write to the sensor registers. But if you change any setting about the measurement, it will affect the result in data register.