title: tmux: hangs after run-shell command and do not respond to any command
body: <p>I have problem with bindings in tmux 1.8.</p>
  
  <p>Problem appear when I type command which run shell
  For example:</p>
  
  <pre><code>bind y run-shell "tmux show-buffer | xclip -sel clip -i"
  </code></pre>
  
  <p>And i type y
  After execution command, tmux not respond on any other bindings (for example w)
  It may take a few minutes and then you can use bindings.</p>
  
  <p>what could be the problem?
  It appeared in version 1.8 (with version 1.7 all ok)
  OS Ubuntu 13.04(64)</p>