title: dict remove also deletes key
body: <p>Tcl’s <code>dict remove</code> does not behave exactly as I expected. (I'm sure it's because my expectations are incorrect)</p>
  
  <pre><code>% set d [dict create]
  % dict set d O1 C1 child1
  O1 {C1 child1}
  % dict set d O1 C2 child2
  O1 {C1 child1 C2 child2}
  % dict set d O2 C3 child3
  O1 {C1 child1 C2 child2} O2 {C3 child3}
  % dict remove $d O1 C1
  O2 {C3 child3}
  </code></pre>
  
  <p>I was expecting the result to be:</p>
  
  <pre><code>O1 {C2 child2} O2 {C3 child3}
  </code></pre>
  
  <p>What's the reason for O1 C2 also being removed?</p>