[Update]
We have released chart v3.10.5 with the above fix. Please refer to the release blog for more information. Do download the latest version from our download page and let us know your feedback.
@jeff,
In axisX labelAutoFit property is set to true by default, which automatically wraps and/or rotates and/or reduces font size of the label when they are too long and overlaps, finds the best-fit and automatically manages label overlapping. It also takes into consideration values of other properties like labelAngle, labelWrap, labelFontSize, labelMaxWidth, etc., based on which labelAutoFit tries to adjust the labels on the axis and may result in reducing the height of the plot area.
You can avoid the reduction in height by setting labelAutoFit property to false as shown in this updated JSFiddle.
—
Shashi Ranjan
Team CanvasJS