<p>The mixed compensatory system (MCS) subtracts single-member district seats from the total number of seats a party earns through list votes to preserve a proportional seat distribution. Yet, ironically, this rule designed for fair seat allocation may enable party exploitation, leading to disproportionate representation. This article explores the paradox of the MCS—which was intended for equitable seat distribution but often benefits parties manipulating the system—through the lens of the “mixed semi-compensatory system” (MSCS) in South Korea. The Democratic Party of Korea, seeking to amend the parallel system, allied with minor parties and implemented a more proportional MSCS in 2019, aiming to foster a multiparty system. Despite these intentions, seat allocation under the MSCS was nearly identical to the parallel system. The Justice Party, a minor party championing this reform, did not gain a single seat in the 21st National Assembly election and won no seats in the 22nd election. We interpret these unforeseen consequences as stemming from the inherent design of the MSCS, which facilitates the creation of satellite parties by major parties competitive in district races.</p>