Steps:

1. Go to Content/ Content structure.
2. Create new content which contains RichText field, e.g. Folder.
3. Add table.
4. In table cell type same text and add line break in the middle (shift+enter). 
5. Highlight typed text and select formatting e.g. bold. 
6. Publish content.

Actual result:  Line break is removed. 

Remarks: Works fine for unformatted table cell.