paragraph styles in .doc

I’m preparing a manuscript for smashwords.com, and they require me to submit a .doc file (not .docx or .odp). According to http://publishinginsider.net/smashwords-style-guide-for-libreoffice-open..., I should be able to set line spacing to ‘single’. However, whenever I change a style from ‘proportional’ to ‘single’, save the file and reopen it, the paragraph style is back to ‘proportional’. Other elements of the style, such as spacing and first line indent, provide no problem.

Suggestions, anyone?

Added note: after some experimenting I found that a new style with spacing ‘single’ cab be arrived from Default style, but not from body text style.
That suffices as a workaround.