Io/console: EBADF by IO#echo?

io/console e$B$Ne(B IO#echo? e$B$,0J2<$N$h$&$Ke(B EBADF
e$B$K$J$k$N$OJQ$8$c$J$$$G$7$g$&$+!#e(B

% ./ruby -rpty -rio/console -ve ‘PTY.open {|m, s| s.echo? }’
ruby 1.9.3dev (2010-05-12 trunk 27763) [i686-linux]
-e:1:in echo?': Bad file descriptor (Errno::EBADF) from -e:1:inblock in ’
from -e:1:in open' from -e:1:in