Ah, I see what the OP meant now.
In that case, the most likely explanation is neither finger trouble nor coding errors on the part of the crews.
LH use alphanumeric callsigns on many European flights, including FRA-MLA, and those callsigns change periodically so that the same timetable flight number can have a different callsign in each successive season, and vice versa.
It would seem that FR24 is misinterpreting one of the FRA-MLA alphanumerics as corresponding to LH442 FRA-DTW.