I can confirm this too on the latest master.

I took a quick peek this morning, and my suspicion is that the problem is somewhere within org-babel-comint-with-output in lisp/ob-comint.el, but I'm not positive at this point.

On Wed, May 5, 2021, at 22:35, John Corless wrote:
> Confirmed
> 
> Daniele,
> 
> I was able to reproduce the behavior you described.  Using the test case...
> 
> #+BEGIN_SRC shell script :results output
> ping -c 1 127.0.0.1
> #+END_SRC
> 
> ... the results output matches what I get in a bash shell.  But if you add the :session to the header args like this...
> 
> #+BEGIN_SRC shell script :results output :session test
> ping -c 1 127.0.0.1
> #+END_SRC
> 
> ... the output line that includes "0% packet loss" gets truncated to after the "%" sign.
> 
> I tested with 9.4.5.
> 
> John
> 
> 
> On Wed, May 5, 2021 at 10:19 AM Daniele Pizzolli <dan@toel.it> wrote:
>> 
>> Hello,
>> 
>> Try to execute a few times the following and see the output corrupted in
>> the line:
>> 
>> #+BEGIN_EXAMPLE
>> 1 packets transmitted, 1 received, 0% packet loss, time 0ms
>> #+END_EXAMPLE
>> 
>> #+PROPERTY: header-args:shell
>> #+PROPERTY: header-args:shell+ :results output verbatim :wrap src text :session test
>> 
>> #+NAME: ping
>> #+BEGIN_SRC shell
>> ping -c 1 127.0.0.1
>> #+END_SRC
>> 
>> I tried to write a test (now with the :expected-result :failed), that
>> hit the problem both in main and master (applies fine to both).
>> 
>> I was not able to fix it, but hopefully the tests are still useful for
>> somebody more knowledgeable!
>> 
>> Thanks for you suggestion/fix!
>> 
>> Best,
>> Daniele
>>