Dropdown menu should be put into a separate toolbar group.

 

Please try the following code:

 

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
 <codeviewToolbars>
  <item type="g_start" />
  <item type="g_end" />
 </codeviewToolbars>
 <toolbars> 
  <item type="g_start" />
  <item type="image" name="InsertUnorderedList" imagename="bullist" />
  <item type="image" name="Undo" />
  <item type="image" name="Bold" />
  <item type="image" name="Italic" />
  <item type="image" name="Underline" imagename="under" />
  <item type="image" name="InsertLink" imagename="link" />
  <item type="image" name="Forecolor" />
  <item type="image" name="Backcolor" />
  <item type="g_end" /> 
  <item type="g_start" />
  <item type="dropdown" name="FontName" width="95" text="[[FontName]]" command="FontName" />
  <item type="dropdown" name="FontSize" width="40" text="[[FontSize]]" command="FontSize" /> 
  <item type="g_end" /> 
 </toolbars>
</configuration>