The first heading is only partially excluded and transformed into content on Include/Display Macro when including a section

STEPS TO REPRODUCE

1. Create a page (e.g. 'Pag1') with the following content:

   = This is Heading 1 =
   
   This is the original page content.

2. Create another page (e.g. 'Pag2')
3. Insert Include Macro 
4. On Page parameter select 'Pag1'
5. Tick the checkbox "Exclude First Heading"
6. On Section parameter insert 'HThisisHeading1'

or paste in source/wiki mode:

{{include reference="Pag1.WebHome" excludeFirstHeading="true" section="HThisisHeading1"/}}

1. Save the page

EXPECTED RESULTS

On 'Pag2', only the content from the section of 'Pag1' is displayed:

This is the original page content.

ACTUAL RESULTS

The first heading is not entirely excluded, apparently being transformed into content: 

 is Heading 1
This is the original page content.