If a new document is loaded and the extension isn't known, Notepad++ defaults to no syntax highlighting. If the Document Map is opened (it shows no syntax highlighting) and then the Language (syntax highlighting) style is changed, the document map does not refresh/update to show the new syntax highlighting colors. In order to update the document map, the document map must be closed and reopened to show the new syntax highlighting colors.

Attached image show "before" with no syntax highlighting in document map, but is highlighted in actual document. "After" shows the document map with highlighting after being closed and reopened.