title: Why diff with ignore matching lines doesn't work as expected?
body: <p>I have the following files:</p>
  
  <p><code>file1.txt</code>:</p>
  
  <pre><code>###################################################
  Dump stat Title information for 'ssummary' view
  ###################################################
  Tab=&gt; 'Instance' Title=&gt; {text {Total instances: 7831}}
  Tab=&gt; 'Device' Title=&gt; {text {Total spice devices: 256}}
  Tab=&gt; 'Memory' Title=&gt; {text {Total memory allocated: 962192 kB}}
  Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 9030 ms}}
  </code></pre>
  
  <p><code>file2.txt</code>:</p>
  
  <pre><code>###################################################
  Dump stat Title information for 'ssummary' view
  ###################################################
  Tab=&gt; 'Instance' Title=&gt; {text {Total instances: 7831}}
  Tab=&gt; 'Device' Title=&gt; {text {Total spice devices: 256}}
  Tab=&gt; 'Memory' Title=&gt; {text {Total memory allocated: 9621932 kB}}
  Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 90303 ms}}
  </code></pre>
  
  <p>And I'm running the following command:</p>
  
  <pre><code>diff -I 'Memory' file1.txt file2.txt
  </code></pre>
  
  <p>which outputs:</p>
  
  <pre><code>6,7c6,7
  &lt; Tab=&gt; 'Memory' Title=&gt; {text {Total memory allocated: 962192 kB}}
  &lt; Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 9030 ms}}
  ---
  &gt; Tab=&gt; 'Memory' Title=&gt; {text {Total memory allocated: 9621932 kB}}
  &gt; Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 90303 ms}}
  </code></pre>
  
  <p>However my expected output is:</p>
  
  <pre><code>&lt; Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 9030 ms}}
  ---
  &gt; Tab=&gt; 'Cpu' Title=&gt; {text {Total cumulative CPU time: 90303 ms}}
  </code></pre>
  
  <p>Note that in the command if I change <em>'Memory'</em> to <em>'Tab'</em> or <em>'Title'</em> problem's solved, but probably all lines are ignored cause they all have Tab and Title.</p>