SharePoint 2010 Ribbon with wrong style in Chrome and Safari

When we add custom ribbon to SharePoint 2010, it may display well in IE but not in Chrome and Safari. The sample xml is below like this:

<Tab Id=""Ribbon.CustomTab"" Description="""" Sequence=""4000"" Title=""测试Ribbon"">
            <Scaling Id=""Ribbon.CustomTab.Scaling"">
              <MaxSize Id=""Ribbon.CustomTab.Scaling.Custom.MaxSize"" Sequence=""10"" Size=""LargeLarge"" 

GroupId=""Ribbon.CustomTab.Group""/>
              <Scale Id=""Ribbon.CustomTab.Scaling.Custom.Popup"" Sequence=""20"" Size=""Popup"" 

GroupId=""Ribbon.CustomTab.Group""/>
            </Scaling>
            <Groups Id=""Ribbon.CustomTab.Groups"">
              <Group Id=""Ribbon.CustomTab.Group"" Sequence=""30"" Title="""" Description="""" 

Template=""Ribbon.Templates.Flexible2"">
                <Controls Id=""Ribbon.CustomTab.Controls"">
                  <Button Id=""Ribbon.CustomTab.Button"" Image32by32=""/_layouts/2052/images/formatmap32x32.png"" 

Image32by32Top=""-320"" Image32by32Left=""-64"" Command=""CustomCommand"" Description="""" LabelText=""Click Me"" Sequence=""10"" 

TemplateAlias=""o1"" ToolTipTitle=""Test"" ToolTipDescription=""Test""/>
                </Controls>
              </Group>
            </Groups>
          </Tab>

We may cost a long time but can't find the reason. Why SP 2010 own ribbon works well in Chrome and Safari?

The reason may be a little disappointing for the Group tag with Title attribute null...

When we set the Title attribute, it works well.