3.15 Future time reference with infinitive postmodifier
Rule: Future time reference can be expressed in the infinitive postmodifier by the progressive, but not by the simple present.
Examples of errors:
She is happy to be married to him can only mean that she is already married to him. Soon in (1) is illogical, then, if the sentence is so understood. The author intended to say, however:
She is happy to be marrying/getting married to him soon.
She is happy that she is going to marry him soon.
In other words, if the infinitive postmodifier refers to a state or event occurring after that expressed by the main verb, the infinitive must be progressive.