How Do I Activate a specific Safari Window using rb-appscript?

I can't get rb-appscript to activate a specific Safari window. It is always activating the most recently active window.

(in irb, assuming rb-appscript is already installed)

require 'appscript'
include Appscript

safari = app 'Safari'
safari.open_location "http://www.google.com"
safari.open_location "http://www.apple.com"
safari.open_location "http://www.bing.com"
safari.documents.URL.get
=> ["http://www.bing.com/", "http://www.apple.com/", "http://www.google.com.ph/", "http://www.apple.com/startpage/"]
safari.documents[1].URL.get
 => "http://www.bing.com/"
safari.documents[3].URL.get
 => "http://www.google.com.ph/"

Now here comes the hairy part. Activating documents[3] sho开发者_运维问答uld activate the google window, but this isn't what is happening.

safari.documents[3].activate
 => nil (activates the bing window instead of the google window)
safari.windows[3].activate
 => nil (activates the bing window instead of the google window)

You can't activate windows:

app("Safari").windows[its.name.eq("Google")].index.set(1)

tell application "Safari" to set index of (windows where name is "Google") to 1