When I create an horizontal bar chart and set one of the datasets to 'line' it doesn't show. I suspect the axis for the line chart is not changed with the parent horizontalBar chart.
I think the expected behaviour is to let the main chart type be leading, in this case the horizontal bar chart, so that the datasets that are provided don't need to be changed.

This example would work with a normal bar-chart, but not with an horizontal bar-chart:
chartData : { labels: [ 'apple', 'orange', 'banana', 'coconut' ], datasets: [ { title: 'Taste', data: [ 1,4,2,3 ] }, { title: 'Throwability', data: [ 5,4,2,3 ], type: 'line' } }