A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 15 May 2015
Battle: Target your unbowed Samurai or Berserker Personality. Bow one or two target enemy units with a total Gold Cost less than your Personality's unit's total Gold Cost. Destroy any cards in the enemy units with 0 Gold Cost.
Interrupt: Target your Yojimbo. The action must target him, if legal.
Player A plays Standing Fast, targeting two units of player B, Isawa X and Isawa Y.
Player B interrupts with Final Sacrifice, targeting a third unit, Shiba Z.
Final Sacrifice requires that one of the two targets of Standing Fast be Shiba Z. But which player chooses which of Isawa X and Isawa Y is no longer targeted?
Alex Jones (rules official), 19 May 2015
Player A plays Standing Fast, targeting two units of player B, Isawa X and Isawa Y.
Player B interrupts with Final Sacrifice, targeting a third unit, Shiba Z.
Final Sacrifice requires that one of the two targets of Standing Fast be Shiba Z. But which player chooses which of Isawa X and Isawa Y is no longer targeted?
Errata has been issued to Final Sacrifice.
The player of Final Sacrifice chooses which targeting choice is changed.