File Staged Content Different from HEAD : <p>When I attempt to use <code>git rm --cached</code> I receive the following error:</p>

<pre><code>error: the following file has staged content different from both the file and the HEAD:
</code></pre>

<p>I know that I can circumvent this error with <code>git rm --cached -f &lt;filename&gt;</code>. But normally when I unstage files with <code>git rm --cached</code> I do not get this error. </p>

<p>My question is what does it mean that the file has different staged content from the <code>HEAD</code>.</p>
