Created attachment 104337 [details] Screenshot and problematic file See the attached (zipped) screenshot and the file that shows the problem. File is from Drupal 8.2.6.
This is not a bug. By default, *.config files seem to be highlighted as LogTalk syntax highlighting. You need to switch to XML via Tools > Highlighting > Markup > XML. You can also persistently change this if you edit the Mode in Settings > Configure > Open/Save > Modes & Filetypes, choose "Markup/XML", and then *.config to the file extensions. You probably also need to raise the priority to beat the LogTalk highlighting.