Why does this add two favourites?

I've tried a number of variations on a startup script that adds a thumbnail to the favourites panel, but in each case the script creates two identical favourites. This was adapted from one in the JS reference:

#target bridge;
app.registerBrowseScheme( "bank" );
var bankRoot = new Thumbnail( "bank://root", "My Bank" );
bankRoot.displayPath = "http://www.adobe.com/";
bankRoot.displayMode = "web";
app.favorites.insert( bankRoot ); //add node

Tried this one too: Robert Stucky, "Bridge script examples" #7, 27 May 2005 1:28 pm

The same happens with each script. Any thoughts?

John