Description:
Heading paragraph styles aren't exported correctly when exported to RTF file format.  See attached screenshots for more details.

Steps to Reproduce:
1. Open LibreOffice
2. Go to File > Templates > Manage Templates
3. Go To Settings > Reset Default Template > Text Document
4. Open new Writer document
5. Paste the following into the document

‘Heading’ paragraph style.
‘Heading 1’ paragraph style.
‘Heading 2’ paragraph style.
‘Heading 3’ paragraph style.
‘Heading 4’ paragraph style.
‘Heading 5’ paragraph style.
‘Heading 6’ paragraph style.
‘Heading 7’ paragraph style.
‘Heading 8’ paragraph style.
‘Heading 9’ paragraph style.
‘Heading 10’ paragraph style.

6. Assign each paragraph the corresponding Heading paragraph style
7. Go to File > Save a Copy, and save as a Rich Text .rtf file
8. Open file in Wordpad, or 'Place' file into an Affinity Publisher document


Actual Results:
In any other applications the text formatting in the RTF file isn't displaying the same as the original formatting (see attached screenshots).

Expected Results:
The text formatting in the RTF file should display with the same formatting as the original file.


Reproducible: Always


User Profile Reset: No



Additional Info:
Windows 10 - 17763.379 (1809)

LibreOffice:
Version: 6.1.5.2 (x64)
Build ID: 90f8dcf33c87b3705e78202e3df5142b201bd805
CPU threads: 4; OS: Windows 10.0; UI render: GL; 
Locale: en-GB (en_GB); Calc: group threaded