MS Word will underscore with wiggly red or blue lines words that are not in the lexicon. When I click on "Ignore" or "Ignore all", the lines disappear. But they reappear after the document is saved, closed, and reopened. I have corrected some documents several times but they revert to the underscored versions seemingly automatically. How do I save the corrections?
"Ignore" doesn't flag the document as "OK", so there's nothing in the document to tell Word that the spelling has been checked and accepted as-is. So you can't "save the corrections", unless you make actual corrections with words it recognizes.
Word will try to spell-check every time you open a document, unless you turn off Word's spell check.
You may also want to check out this similar SU question: