Word document Font reverts

Re: Libre Office Writer on WIN 10 & XP
I have a big problem getting the document to stay with the selected font in some particular passages. I highlight and swap the typeface (font) to Comic Sans and it appears on screen OK. However once stored and re-opened some passages revert to a different font. It can be just parts of a whole paragraph. The majority of the document is OK but certain passage will not maintain my choice once stored and then re-opened. I am absolutely unable to get this problem sorted. I have even tried the document on a totally different machine with same result.
OS - Win10 - WINXP - same result
What on earth am I missing here? How can I get this sorted out PDQ?
Rgds & thanks,

In which format do you save your document? If doc, try with odt. Also, direct formatting is always a source of trouble, you need to learn how to use styles.

I absolutely second RGB-es. Work only in ODT. Modify the style font (or create a style as necessary), not the paragraph font. Remove direct formatting.