Your understanding is wrong. Nazi Germany never issued War Bonds to the public. They did however borrow money from banks using war bonds as collateral and forced banks and financial institutions in annexed and occupied territories to "buy" war bonds. I believe they were considered default after the end of the war, unlike bonds from WW1 which I believe where honored and repaid along with other debts in the 1953 London Debt Agreement. It is possible that these bonds were in fact redeemed in 1948 along with other debts to the private secotor* but I have been unable to verify that.

*With the reintroduction of the Deutsche Mark (DM) as currency in place of the defuct Reichsmark (RM) money was converted at different exchange rates. Essential payments (wages, rents, pensions etc.) were exchanged at a 1:1 rate, 10:1 for non-bank credit balance and 10:0,65 for all other RM holdings. If the war bonds were redeemable it would probably have been at a 10:0,65 rate meaning that the 500 RM war bond would have been redeemable for ~32 DM. That said, I don't believe this was the case. I believe war bonds were cancelled along with most other claims by banks against the state in 1948 on October 4th. This would have included the private savings accounts that were "converted" to war bonds during the war, essentially wiping out a lot of private savings.