R' Dov Kay wrote:
> I recall seeing that R. SZ Auerbach in Halichos Shlomo also
> paskens that one does not make a new b'rocho in this case.
> Can't remember his sevara, though.

Halichos Shlomo, Tefilah 3:14 says: "If ones tallis fell during 
Tefila, when he goes back and puts it on he does not say the bracha, 
even if it fell entirely off, but if it fell after the end of the 
Tefila he does have to say the bracha."

The notes there explain: A tallis ought to follow the same halacha as 
in Mishne Brura 25:44, which says that nowadays, if the tefillin 
moved from their place during Tefila, we do not say a bracha when 
replacing them.

He also quotes MB 25:43, which says that if when saying the bracha on 
his tefilin, he had in mind that he'd be taking them off and 
replacing them several times that day, this too eliminates the need 
for a bracha if the tefillin happened to move from their place. 
Therefore, he concludes, "it's pashut that nowadays, when everyone 
normally wears a tallis, and it is embarrassing to sit without one. 
As it is explained in [Shulchan Aruch] 13:3, it is a kavod habriyos 
situation, so everyone holds we don't make a bracha unless it fell 
after the Tefila ended, because when he first put it on, he certainly 
had it in mind to wear it for the entire Tefila, and such is the 
minhag."

(Based on this reasoning it is clear to me (though others might 
disagree), that when he referred to the end of the Tefila, he did NOT 
mean the end of Shmoneh Esreh, but that he meant the end of the time 
when it is normal to wear a tallis, i.e. the end of Shacharis/Musaf.)

Akiva Miller