When a break tag is entered between an opening and closing paragraph tag the break tag is removed. This occurs when using a rich area text field and has been tested with CU11 applied.
As part of the content cleaning process the editor can remove tags in some cases. While this is usually a time saver, in this case it can remove a tag you wish to preserve.
Please note this is not an official fix. You should do quality assurance testing for all code changes to ensure existing functionality is preserved.
1) Remove or comment out line 153(this may vary by version, tested in 9.1SP1 CU11) in contentoutgoing.xslt.