Macro is duplicated when trying to remove underline style

Follow this steps to reproduce:

• switch to source tab
• set the content to:

  __before {{html}}center{{/html}} after__
  

• switch back to WYSIWYG tab
• select the macro by clicking on it
• click the underline tool bar button

As a result the macro box is split, the underline style is not removed and the wiki syntax is:

__before {{html}}center{{/html}}__{{html}}center{{/html}}__{{html}}center{{/html}} after__