Data reduction is overly aggressive if marker.enabled set to null in bubble chart

[DCIP]

Expected behaviour

Setting marker.enabled to null in a bubble chart should result in the same chart as when marker.enabled is not set (the docs state the default value for this parameter is null).

Actual behaviour

When bubbles in a series share the same x value they are not rendered, if marker.enabled is set to null. However, they ARE rendered if marker.enabled is left to default its value.

Live demo with steps to reproduce

http://jsfiddle.net/c83uLbfh/

Affected browser(s)

Tested in Chrome