In ClassFileFormatVersion.java:

 * @since 20
 * @see System#getProperties System property {@code java.class.version}
 * @see java.compiler/javax.lang.model.SourceVersion

In ClassFileFormatVersion.html:

                    <dt>See Also:</dt>
                    <dd>
                        <ul class="tag-list-long">
                            <li>
                                <a href="../System.html#getProperties()">
                                    <code>
                                        System property
                                        <code>java.class.version</code>
                                    </code>
                                </a>
                            </li>

This generates a nested <code> tag, which is reported.