The setData method automatically sorts x-keys, but it's problematic in some cases, particular when parseTime: false is speficied.

Given this data,

Morris.Line({
  element: 'demo',
  data: [
    {x: '9:30am',  y: 10},
    {x: '9:45am',  y: 20},
    {x: '10:00am', y: 30},
    {x: '10:15am', y: 40},
    {x: '10:30am', y: 50},
  ],
  xkey: 'x',
  ykeys: ['y'],
  labels: ['ever increasing'],
  parseTime: false
});

We get this chart.

Notice that the leftmost x-key becomes 10:00am, where it should have been 9:30am.

Btw I had hard time figuring this out... users reported this problem but it only occurred when the x-keys span between 9:59am and 10:00am. :)

I think when parseTime: false is specified, automatic sorting on x-keys should be disabled, as the doc says:

Set to false to skip time/date parsing for X values, instead treating them as an equally-spaced series.

So it makes more sense to leave X values as they are.