Why do the following reactions proceed differently?

Pb₃O₄ +8HCl --->3PbCl₂ +Cl₂ +4H₂O
Pb₃O₄ +4HNO₃ --->2Pb(NO₃)₂ +PbO₂ +2H₂O

Pb₃O₄ is a stoichiometric mixture of 2 mol of PbO and 1 mol of PbO₂. In PbO and PbO₂ the oxidation state of lead is +2 and +4 respectively. PbO₂ thus behaves as an oxidising agent and therefore can oxidise Cl^- ion of HCl into chlorine. Also, PbO being basic in nature, therefore the reaction
Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O
can be split into two reactions namely:
(a) Acid-base reaction
     2PbO + 4HCl  →  2PbCl₂ + 2H₂O
(b) Redox reaction
 +4          -1          +2    0
PbO₂ + 4HCl → PbCl₂ + Cl₂ +2H₂O
Since HNO₃ itself is in oxidant, therefore, the reaction between PbO₂ and HNO₃ is not possible. However, the acid-base reaction occurs between PbO and HNO₃ as:
2PbO + 4HNO₃ → 2Pb(NO₃)₂ + 2H₂O
                                       (acid-base reaction).
It is the passive nature of PbO₂ against HNO₃ that makes the reaction different from the one that follows with HCl.