This paper discusses the issue of quantization damage in Top-k Mixture-of-Experts (MoE) routing. Due to the discontinuity of MoE routing, numerical disturbances (such as 4-bit KV-cache quantization) can cause tokens to cross decision boundaries and trigger expert flips. The authors propose a causal apparatus, empirical findings, and a detection-limit result. The experiment results show that about a third of the damage is routing-mediated (RMF ~ 0.31). The router margin can detect flips (AUC 0.772) but cannot distinguish between harmful and helpful flips. The empirical results confirm the signed-flip tax and sign-inseparability, and the clean-reference remedy's payout is modulated by architecture. In summary, this paper explores the issue of quantization damage in MoE routing, proposes detection and analysis methods, but also points out the difficulty of repairing the damage. Blogger's Review: This paper reveals the issue of quantization damage in MoE routing, providing new insights with its causal apparatus and empirical findings. However, the difficulty of repairing the damage remains, requiring further research and development.