TkOptionMenubutton

When I try the attached script, I get the following error. Using recent ruby
1.8. Could something please confirm that this is a bug… or am I doing
something wrong? The error is:

C:/ruby/lib/ruby/1.8/tk.rb:3615:in initialize': undefined methodkind_of’
for nil (NoMethodError)
from /t.rb:4:in `new’
from /t.rb:4

The script is:

require 'tk’
val = TkVariable.new
options = [‘one’,‘two’,‘three’]
TkOptionMenubutton.new($root, val, *options)