Just when you thought you were safe to use Model Ms, turns out
Maxiswitch are a pretty evil lot.Another interesting thing - the source here mentions that Maxiswtich opened up shop in Mexico in 1994, which is around the same time that the M13s and M15s it's noted for came on the market. But there are Mexican IBM keyboards which predate this.
Take a look at this for example. Note that it has no Maxiswitch markings, but is rather described as being made by "IBM Mexico". Did IBM have their own keyboard factory in Mexico? Was it sold to Maxiswitch, or was the Maxiswitch plant a completely different one?
EDIT: Turns out that IBM had a big manufacturing plant in Mexico, but it was located elsewhere in Mexico, so it wasn't as if it was the same place.
Main point here is that not all Mexican Model Ms are Maxiswitch made ones.