Bash – Whenever I type some wrong command, the terminal tries to run that command in the background

There are several ways a process might be killed because of a dying terminal.

1. The first way is that the terminal driver in the kernel sends a SIGHUP signal to the controlling process for which the terminal is the controlling terminal. In most cases, the controlling process is the shell that is initially started in the terminal, and its controlling terminal is the one that its stdin, stdout and stderr are connected to. A process becomes disconnected from the controlling terminal if it calls setsid.

2. The second way is that the shell, when it receives SIGHUP, re-sends that signal to its subprocesses — more precisely, to its background jobs. Some shells (ksh, bash, zsh) have a disown builtin to tell the shell not to send a SIGHUP to a particular job.

3. If the terminal goes away and a program tries to read from it, it is notified of an end-of-file condition (or possibly EIO for a background job). If the terminal goes away and a program tries to write to it, the write returns with an EIO error. These might cause the program to exit.

So what su changes here is that (2) would normally cause the initial shell to kill the background job, but since that background process is running as a different user, the signal cannot be delivered, and the background process lives on.

You have a terminal (or terminal emulator) which understands multibyte encodings (probably UTF-8), but a shell which doesn't. Try setting the environment variable LANG to C.UTF-8. Or run locale -a to find another likely value to try.