Spoon probably already knows this, but this occurred because the tokens added by Far sight don't trigger the keyword effect. Playing Stalker set the Undead tokens to 75, and then Far sight attempted to add an additional 30 after that.
However, the way this was previously explained, it sounded like the effect -is- supposed to occur if the Far sight card itself has the keyword. It seems like an additional check should be added when the Far sight effect occurs.
This doesn't come up a lot because, until the last update with the addition of Far sight and the card Trickster, there wasn't any benefit to having fewer than three token types selected. As people test and adjust their decks, it's happening more often that a deck is optimized with only one or two set. Without that mostly-unused third keyword choice, it's much more likely that the "lowest token counter" is a value close to 100.