WFM Schedule Publish Fails with 409 Conflict on Shift Swaps

Why does the POST /api/v2/wfm/schedules endpoint returns a 409 Conflict when publishing schedules that include pre-approved shift swaps in v2024.1? The swaps are validated in the agent portal, yet the API rejects them claiming overlapping availability rules. This happens consistently in the Chicago environment during weekly publishes. Are shift trades excluded from the bulk publish payload, or is there a specific flag required to handle them?