是平台的bug, 后续版本将解决。当前版本你可以这么做：
修改/UI2/system/components/html/designer/html.xml文件中关于ul和li的定义， 改为下面的格式：

 <element name="ul(html)" tag-name="ul" icon="span.gif" text="ul" canAddChild="true"
 
 component-class="UL" child-range="li(html)"
 component-type="layout-container" >
 <properties>
 <property name="xid" text="编号" />
 <property name="class" text="class" editor-extend-data="xui-ul:ul"/>
 <property name="dir" editor-ref="edit-dir" text="文本方向" />
 <property name="lang" text="语言代码" />
 <property name="style" text="样式" editor-ref="styleDialog"/> 
 <property name="title" text="额外信息(可在工具提示中显示)"/>
 <property name="xml:lang" text="XHTML语言代码" />
 <include path="$UI/system/components/designerCommon/commonConfig.xml#//common-properties/group[@name='bind']"/>
 </properties>
 
 <events>
 <include path="$UI/system/components/designerCommon/commonConfig.xml#//html-evens/*"/>
 </events>
 
 <templates>
 <template name="default"><![CDATA[ 
 <ul></ul>
 ]]></template>
 </templates>
 
 </element>

 <element name="li(html)" tag-name="li" icon="span.gif" text="li" canAddChild="true"
 
 component-class="Li" parent-range="ul(html)"
 component-type="layout-container" >
 <properties>
 <property name="xid" text="编号" />
 <property name="class" text="class" editor-extend-data="xui-li:li"/>
 <property name="dir" editor-ref="edit-dir" text="文本方向" />
 <property name="lang" text="语言代码" />
 <property name="style" text="样式" editor-ref="styleDialog"/> 
 <property name="title" text="额外信息(可在工具提示中显示)"/>
 <property name="xml:lang" text="XHTML语言代码" />
 <include path="$UI/system/components/designerCommon/commonConfig.xml#//common-properties/group[@name='bind']"/>
 </properties>
 
 <events>
 <include path="$UI/system/components/designerCommon/commonConfig.xml#//html-evens/*"/>
 </events>
 
 <templates>
 <template name="default"><![CDATA[ 
 <li></li>
 ]]></template>
 </templates>
 
 </element>