Same voltage value on every channel: 4-Channel 16-Bit ADC for Raspberry Pi (ADS1115)

I followed the instructions from the wiki:
But when I call the voltages via the /sys/bus/iio/devices/iio:device0/in_voltage_x_raw and scale it by the corresponding scale values, I get nearly similar voltages for non-used AINs.
In this example, only the AIN0 and AIN2 are used.
But I receive the following values for AIN0-AIN3:
0: 0.521625
1: 0.5615
2: 0.5215
3: 0.56425

The voltages are right for pin0 and 2, but they should be 0 for the other pins.
What am I missing?