Created attachment 120484 [details]
This issue can be easily reproduced using the following steps:
1. Create a new document, apply some styles there (I used Heading1 and Heading2), and save it as RTF. Just in case, I have attached my test document.
2. Close the document.
3. Open it again and save as ODT.
4. Press Clear Direct Formatting and save the document.
That's all. Next time you open the document styles (in my case, Heading1 and Heading2) are not applied anymore.
I am using version 18.104.22.168 on Arch Linux
Seems to be a duplicate.
But the test file is nice to have.
*** This bug has been marked as a duplicate of bug 47471 ***