I am not fond of this default behavior
The chart behaves much like the excel chart, where the range is based on the values it presents. There is a notion of a delta - the delta is the difference between the max and min values. If the delta is less than six times smaller than the max - the chart includes the zero (if (max / delta < 6) IncludeZero). An exception is made when the delta is 0, which is the case you are interested in. In this case, it makes no sense to include the 0, because the value could be 10 billion. If later you add another item with value 10 billion and one, the chart will chose a range (10 bil, 10 bil + 1), so having the zero would make no sense.
This is why by default if the delta is 0, we show a range ~(+0.5, -0.5) around the value. To make sure the zero is part of the range - the proper way to go is to set the Minimum to zero, this is by design.
I could still see undesired results
If you inform us about these, we might be able to help, or if you think that there is a bug, or a better way to display the range, please let us know.
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