1. By "borrow", I don't mean sentence (2) should read: I heard John talkED to her. This is obviously wrong.
2. Similarly, sentence (3) is not meant to read as: I heard John WAS talking to her. Although grammatically correct, it gives a meaning different from the original sentence (3): "I heard John talking to her" is not the same as "I heard (that) John was talking to her".
3. What I meant was not a substitution of the verbs, but John TALK (sentence (2)) is in the PAST (because "heard" is in the past); and John TALKING is also in the PAST (again because "heard" is in the past) but the -ing indicates that at the time that I heard it, John was then talking (in progress).
4. This "borrowing" can only happen when "John" (object of heard) is the subject of "talk" (infinitive) or "talking" (cont participle).
5. Compare: "I heard (that) they ARE coming": "heard" is simple past, "are" is present + "coming" is continuous. The two verb constructions "heard" and "are coming" are in different tenses but not in conflict, neither is any "borrowing" involved because they are in different clauses.