Output of run script not getting flushed

Hi all,

I'm experiencing a problem of application output not showing up until it has finished (or probably until the stdout buffer is full).

run:
> #!/bin/sh
> exec 2>&1
> exec python -c "while True: import time; print time.time(); time.sleep(0.2)"

log/run:
> #!/bin/sh
> exec setuidgid nobody multilog t s5000000 ./main

Then, `tail -F log/main/current` should constantly print around 5 lines per second, but nothing to be seen. In my Python-based production application, we can see output only once it finishes.

These are the things I tried:
- `python -u` (unbuffered) resolves the issue but feels like a hack, since usually output should be line-buffered, right? And we have daemontools working for many other use cases where things work as usual, i.e. output flushed line-by-line.
- C program doing the same while loop has the same issue
- `exec cat -u >>./main/current` as log program shows the same issue
- `python -c ... | cat -u` (without `exec`) as run program shows the same issue
- OS and package versions where I observe the problem: FreeBSD 9.1, FreeBSD 10.3, Raspbian GNU/Linux 9.6 (stretch), all using daemontools 0.76

Is this something stupidly simple, maybe?

Cheers,
 Andreas