Hi Jim
Just tried this in VW2016.
Attempt 1: Halfway through creating the stair I get a message saying: 'A Script error has occurred. Refer to the file "Error Output" for a further explanation' and lost all ability to edit the stair settings in Vectorworks, even a new stair.
Attempt 2: Following rebooting of VW, it now seems to have worked, and can edit the stair without it disappearing. Few issues with some classes not showing through where supposed to but eventually got it looking like the original 2015 drawing.
Is the custom stair tool due to be updated for next service pack of VW2016? As said before, it has better control (winders, angles etc) than the basic stair tool.