When rendering charts as SVG on the server using PhantomJS, it appears to always use highstock.js, regardless of the Constructor parameter. You can see this on the demo site: http://export.highcharts.com/demo.
Set the Image File Format to SVG. Generate the image as Chart and as StockChart. Look at the SVG that is generated. Both will have a description of "Created with Highstock 2.0.4". Shouldn't Chart result in a description of "Created with Highcharts 4.0.4"? That's what I see when I generate charts via my website using hightcharts.js.
As an experiment, I edited the highcharts-convert.js file. I edited line 24 to use highcharts.js instead of highstock.js. This caused the resulting SVG to have the description I would expect, i.e. "Created with Highcharts 4.0.4". So is the Constructor parameter not working correctly?