I wrote a console command which makes use of the setHidden feature to enter passwords.
When I wanted to test this command I came across a strange issue. My phpunit was stopping and hanging in the hiddeninput.exe process. Obviously the console was waiting for input.
hiddeninput.exe ignored my input given by

$command->setHelperSet($this->getHelperSet("SomeRandomInputString\n"));

I then was able to "unfreeze" my console by just giving the desired input to the console (just pressing enter in this case).

I uploaded an example project which comes with a command and a test to show this issue.
Just clone it, run composer install and phpunit to reproduce:
https://github.com/Fuzzyma/hidden-input-bug

PS: A pic showing what my console is doing:

At the bottom you can see the process which runs at the moment