Why won't Numbers allow me to reset the maximum or minimum on a date-based x-axis?

Question

I have a scatter chart in which the x-axis is dates.  When I first set up the chart everything works, but when I try to change the x-axis minimum or maximum, Numbers seems to go haywire. When the chart is first set up the inspector shows the x-axis minimum and maximum as "auto". If I then try to enter a new x-axis minimum (starting date), as soon as I click in another box in the inspector, Numbers arbitrarily changes the date I have just entered.  I have occasionally been able to extend the chart by changing (increasing) the x-axis maximum, but then if I try to change the minimum, the maximum suddenly changes to equal the minimum and I get a chart with the same date across the x-axis.  There seems to be no rhyme or reason for the way Numbers changes things.  Occasionally I have managed to change both dates in the way that I want and the chart looks good, only to have Numbers do the arbitrary changes when I close the inspector.  I would really like to quit using Excel, but as long as Numbers plays these games that day will never come.  Any help would be appreciated!  Thanks.

Answer 1

Many thanks for you responses.  However the chart is set up correctly, and I did notice that Max is above Min in the inspector. 
Here's what happens:
Here is the chart with the inspector open before I enter a new minimum.
Here is the chart with the new minimum entered, and it's looking good:
Now here's what happens when I close the inspector. All I have done between the above screenshot and the one below is click on the red button on the inspector to close it.
As you can see the minimum has suddenly been arbitrarily changed.
Now I have discovered a workaround which corrects this.  That is to now choose "Undo" in the Edit menu and, voila, the desired minimum is back.
The above is the simplest of the strange behaviors.  If one changes both the minimum and the maximum it gets stranger still, and if one keeps on trying to correct things by again and again applying the desired minimum and maximum via the inspector (without doing the Undo trick) one eventually gets a chart with the x-axis as a single date, i.e. the minimum and maximum are identical.
I'm happy now that I know how to get what I want, but Apple needs to look into this!