At the limit, financial assets should simply mirror banknotes on the liability side of the central bank’s balance sheet. But institutional arrangements do matter. Prior to the crisis, the Federal Reserve (Fed) dealt with a small number of counterparties and mostly held Treasuries directly on its balance sheet.
If and when such phenomena are identified, it is important for all parties  “Asymmetric shocks and risk sharing in a monetary union: Updated evidence and policy implications for Europe”, CEPR Discussion Paper No 4463.