Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0
I can't reproduce the problem by running 'emacs -Q' with emacs 24.5 or any later
version. I tried running your code in *scratch* by typing C-j after the two
expressions. The latter one signaled a Lisp error (void-function loop). If I
replaced "loop" with "while t" the program output a lot of numbers and stopped
promptely when I typed C-g. I was running on Fedora 25 x86-64. Perhaps you could
help move things forward by giving precise instructions on how to reproduce the
problem from a freshly running "emacs -Q".