The German sentence
Die falle schnappte zu.
triggers two different rules. One of the rules should only mark 'falle', the other one 'falle schnappte'. Actually 'falle schnappte' is underlined. Now the suggestion 'Falle' from rule 1 is applied to the marked sequence 'falle schnappte' from rule 2, resulting in an undesired deletion of the word 'schnappte'. This behavior is very confusing.