Not sure if we want to worry about this, but it puzzles me: Users often suggest words that have already been added to spelling.txt. Recent examples include the words “Milliamperestunden” and “Konzeptionerin” (both were added to spelling.txt relatively recently).
When I test the words on languagetool.org, they are accepted by the spell checker.
It’s probably from rechtschreibpruefung24.de - they also have this feature and link it to our site, but they’re not always using the very latest API. If it starts to become annoying, we can ask them to take that feature down.