Using emacs 21.4, ruby-mode.el from Ruby 1.8.5 (byte-compiled), if I
open a file with the following code ...

def foo
  x /= y
   bar
end

...move the cursor to the word "bar" and press Tab, nothing happens!
If I replace "/=" with "*=" then Tab fixes the indentation as I'd
expect.

Any suggestions for debugging this?  I've hacked elisp a few times but
major mode definitions are beyond my experience.

Regards, 

Jeremy Henty