Process does not terminate after 'interact'

[rovf]

This is a small program demonstrating the problem:

require 'expect4r'
require 'misc/shell'
cmd='ssh -2 -i my_key_file.prk -l my_user some_host'
sh=Expect4r::Shell.new
sh.spawn(cmd)
sh.interact
puts 'FINISHED'

The program works fine so far; it logs into the remote host, and interact lets me communicate with the host. I then type 'exit' to leave the ssh shell, and type Control-T to terminate the interaction. The program outputs 'FINISHED'.

However, I don't get a prompt anymore, and no matter what I enter, I see no response. Only if I enter Control-Z to stop my process, I get back to the prompt.

Environment: Windows 7, Cygwin, Ruby 1.9