The problem is, when user uses SHIFT-ENTER to create line breaks, and not an ENTER. Then you'll have many many soft-linebreaks to remove. Doing it by hand is a simple, but time wasting task. Fortunately we have a Find&Replace tool in OOwriter which will help us.
What we have to do?
1) Open Find&Replace tool
2) Show more options
3) Use regular expressions
4) In "Find" put '\n' (without quotes)
5) In "Replace to" put '\n' (without quotes)
6) Replace all. And THAT'S IT! All SHIFT-ENTER breaks will turn to hard linebreaks.
Uff. Then I have more time for coffee breaks:)