When process is detached, the parent process may finish before the detached process (most of the time). In such cases, the pipe set to current ports are closed on parent process and if detached processes output to current port, then the outputs go nowhere.
Proposal to resolve this issue:
sys-process-callto accept extra keyword argument to specify where current ports are redirected.
sys-process-callshould redirect detached processes current ports to standard input/ouput.
The first one is preferable.