Some characters other than letters and numbers suddenly stopped matching the keyboard's key caps until reboot. It turned out to happen after I had pressed the laptop's Fn (unnumbered function) key and an unnoticed other key (probably because Fn is next to the left Ctrl key cap). It seems some key combination with Fn causes a codepage change, such as from US to Spain. An OS desktop panel icon shows the change, and changing back is easy. I don't know if the key combination is defined in software or firmware, so I don't know if it's a feature in Porteus Linux or in the Lenovo laptop, but it is apparently application-independent.