Illustrator Scripting :: Choose Folder Default Location

Any way to allow a user to choose a folder from a default location. I thought I had found the solution but it's not quite working as I wanted:
 
#target illustrator

//Example 1
var output_folder = Folder.selectDialog ('Choose PDF output folder.');

//Example 2
var myFolder=Folder(app.activeDocument.path).selectDlg("Choose PDF output folder:");
 
If I use the code in example 1 the choose folder dialog appears and the 'Open' button is available and when I press the button the location is chosen as expected. However if I use the code in example 2, although the choose window opens in the path of the active documents location the 'Open' button is not able to be pressed until I select a folder., which means that the chosen location is not correct. I should indicate that I'm running this code on a Mac.
 
Any way to have a choose folder dialog window specify a location and be able to select that.