We analyze 72.1 million transactions executed on Kalshi, a CFTC-regulated prediction market, from June 2021 through November 2025. Aggregate prices are well calibrated, but calibration conceals a persistent internal transfer. Because YES and NO positions at the same cost basis risk identical capital for identical payoffs, neither risk preferences nor misperception of the probability level can price them differently; in the data, YES contracts underperform NO contracts of equivalent cost basis by up to 64 percentage points, concentrated at longshot prices. Demand responds to the affirmative framing of the event itself; we term the premium this flow pays the optimism tax. Decomposing returns by order-book role identifies who collects it: liquidity takers earn mean excess returns of -1.12% per trade while makers earn +1.12%, and maker returns are statistically and economically indistinguishable across position directions, indicating accommodation of biased flow rather than superior forecasting. An exact decomposition of taker losses attributes roughly three-quarters of the transfer to execution within price-direction cells and the balance to the accommodation of directionally tilted flow; selection across price levels, the longshot bias proper, contributes essentially nothing. The transfer ranges from 0.17 percentage points in financial contracts to more than 7 in media and geopolitical categories, and it emerged only after post-election volume growth attracted professional liquidity providers: the maker-taker gap reversed by 5.3 percentage points. The forecasting accuracy of prediction markets derives not from the rationality of individual participants but from a microstructure in which liquidity provision monetizes behaviorally biased order flow.