Does the imam's lengthy recitation of "Sami'a Allahu liman hamidah" invalidate the prayer?

The jurists have agreed upon the pillar-status of the opening takbir (Takbirat al-Ihram), and that whoever makes a linguistic error in it that changes the meaning, or adds or omits a letter, his prayer is not valid. As for the transitional takbirs, the tasmi' (saying "Sami'a Allahu liman hamidah"), and the tahmid (saying "Rabbana wa lakal-hamd"), they are sunnah according to the majority of scholars. Thus, whoever intentionally omits the transitional takbirs, his prayer is valid according to them, and likewise for whoever makes a linguistic error in them. A linguistic error that does not change the meaning, such as an error in the tasmi' by saying "Rabbana lakal-hamd", is disliked but does not invalidate the prayer. It is appropriate to advise the Imam and teach him the prescribed tasmi'.