At my place of work we have those machines. So I tested it with some suitably small but still quite legible numbers: and it does replace numbers!
Now typewriters surely never would do such a thing. (Surreptitiously swapping out two typeslugs on a typebar, imagine that for a moment. Though some dial-a-type machine could probably pull off something unexpected.)
Come to think of it, is this an early sign of the singularity? Is Skynet quietly beginning to sabotage?