--- Comment #1 from Jamie Gritton <[hidden email]> ---
Without yet trying to duplicate anything, I see a possibility: PAM. The
difference between "ls" and "ls -l" is the latter looks up users. The
difference between "jexec" and "jexec -U root" is that the former (the default)
looks up users inside the jail. So it seems at first glance that looking up a
user gives you a bad system call.
While your libraries are necessarily all the same, your configurations may not
be. Is it possible that the PAM config on b3 is calling some library that b1