no prompt when reading chars

[Emilio Lopes]

Start a fresh Emacs:

   % ./src/emacs --no-init-file --no-site-file

Now press e.g. "C-x r w" (`window-configuration-to-register')
*slowly*, i.e. with more than `echo-keystrokes' seconds of pause
between the key presses.

Instead of the expected prompt "Window configuration to register: "
you'll see "C-x r w-".

Can someone else reproduce this?