MIF Filter: character tags are not properly encoded on conversion to string literals with additional style formatting

Original:

   <Font
    <FTag `'>
   > # end of Font
   <Char Tab>
   <String `ParaLine 2.'>
   <Char Tab>
  > # end of ParaLine

Merged:

   <Font
    <FTag `'>
   > # end of Font
   <String `    ParaLine 2. '>
  > # end of ParaLine

Expected:

<Font
    <FTag `'>
   > # end of Font
   <String `\tParaLine 2.\t'>
  > # end of ParaLine

A sample document is attached.