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, 4 December 2009
In a recent game with a friend, a point of contention arose regarding the effects of Shameful Injury. During my Action phase, I'd attached a weapon (a Gumbai-Uchiwa) to my personality (Matsu Benika Exp 2), then declared an attack. In the battle, my opponent played Shameful Injury on Benika. He claimed that Shameful Injury would negate the Force bonus to Benika from the item because it had been attached that turn. I contended that the Force bonus was not due to an action (i.e., Limited, Open, Battle, or Reaction), but an item, and thus would not be affected by Shameful Injury.
Gumbai Uchiwa Tessen * Weapon 3G +2F +0C After this card leaves play: Remove it from the game. Battle: If this card is in your discard pile: Attach it to your target Personality.
Shameful Injury Strategy 0G Battle: Even if you control no units at the current battlefield: Negate all current Force bonuses and penalties a target Personality has received from actions. Until the turn ends, negate all new Force bonuses or penalties to him from actions.
Zen Faulkes (rules official), 4 December 2009
In a recent game with a friend, a point of contention arose regarding the effects of Shameful Injury. During my Action phase, I'd attached a weapon (a Gumbai-Uchiwa) to my personality (Matsu Benika Exp 2), then declared an attack. In the battle, my opponent played Shameful Injury on Benika. He claimed that Shameful Injury would negate the Force bonus to Benika from the item because it had been attached that turn. I contended that the Force bonus was not due to an action (i.e., Limited, Open, Battle, or Reaction), but an item, and thus would not be affected by Shameful Injury.
Gumbai Uchiwa Tessen * Weapon 3G +2F +0C After this card leaves play: Remove it from the game. Battle: If this card is in your discard pile: Attach it to your target Personality.
Shameful Injury Strategy 0G Battle: Even if you control no units at the current battlefield: Negate all current Force bonuses and penalties a target Personality has received from actions. Until the turn ends, negate all new Force bonuses or penalties to him from actions.
Bonuses from items are not from actions, and not affected by Shameful Injury.
http://rules.l5r.com/CE_Effects#Source_of_effects: "Targeting, costs, effects and actions come 'from,' or are done by, the card where the thing in question is originally physically printed."