SUMMARY
If I switch to a different tty from the one a Konsole window is on, I find that any child processes producing output get blocked after a certain amount is produced.

STEPS TO REPRODUCE
1. Login on a virtual console (e.g. tty1).
2. Prepare a way to get output from a process. The way I did this was:
  $ mknod /tmp/test.pipe p
  $ cat /tmp/test.pipe
3. Start a graphical session, or switch back to one.
4. Start a terminal emulator, such as Konsole, and do something in it that both produces output on stdout, and sends it to the VC:
  $ for ((i=0;;i++)); do echo $i; sleep 0.005; done | tee /tmp/test.pipe  # sleep is optional, but recommended.
5. Switch back to the VC, and watch the output.

OBSERVED RESULT
When using Konsole, after a couple thousand lines, the output pauses. Only once I switch back to the graphical session, does output continue. I tried this also with xterm and LXTerminal (since they happen to be installed), and this behavior does not occur with them (unless their buffers are just really huge).

EXPECTED RESULT
Not being in the active tty should, I believe, not affect child processes simply because of their terminal output. This is a problem if running an application under Konsole that's doing something important while writing to stderr/stdout.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.15.0-gentoo (64-bit) [custom config]
(available in About System)
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
A workaround seems to be to run things that need to avoid being blocked under something like screen or tmux, since they take over as the controlling terminal, and keep running even if their front-end disappears.