Eggcorns (Wikipedia / YouTube video by RobWords) are language mistakes that sometimes take over and change the spelling and perhaps even the meaning of a word. This is rare in German because there’s fewer homophones but in this episode of Wort der Woche, DW explains how “munttot” became “mundtot”. Available as audio or transcript.
A (natively German-speaking) family member of mine told me that in their childhood, they were surprised that “Folgetonhorn” didn’t start with “Voll-”.