When you use Finnish keyboard, you have to hold Alt Gr down to type | or \ or
certain other characters. When typing a shell command, you may often want to
enter a space character after such characters. But it easily happens that Alt
Gr is still down when you press space, and consequently you type non-breaking
space character U+00A0 (at least, if you use UTF-8 keyboard layout, which is
default in Ubuntu).

https://bugs.launchpad.net/ubuntu/+source/xkeyboard-config/+bug/218637