Pie Chart select state border width across different versions of highchart library should work correctly.
In v4.2.1 of highchart library, there is no need to give initial borderWidth in series options for select state borderWidth to work; i.e. upon selecting pie slice, width of border is applied only after select. But in the latest highchart library, borderWidth in series options needs to be given for borderWidth of select state to work.
Latest version http://jsfiddle.net/kvv2gtj3/2/
Thank you for reporting the issue.
Use CSS to change selected state: http://jsfiddle.net/kvv2gtj3/3/
Fixed #6003, regression with pie chart selection border width.