I guess it must enable the creation of lead carbonate, lead shot also reacts with PVA.
From a miniatures blog entry on 'lead rot':
"The chemical process is: Acetic and some other acids, in the presence of carbon dioxide, catalyze with lead
to produce lead acetate and lead hydroxide. Lead acetate and lead hydroxide together react with carbon dioxide
and form lead carbonate. Lead carbonate then releases acetic acid and the process becomes self-sustaining.
It is important to recognize that the formed lead carbonate is not just a substance clinging to the surface of a
casting, it is the surface of the casting transformed to powder. For practical purposes, a portion of the lead is
gone and lead carbonate is left in its place. The lead carbonate releases acetic acid which can continue the
process until the lead part is progressively consumed from the outside."
Evidently a major culprit in starting the process is wood:
"Wood exposed inside display cases with relatively stagnant atmospheres will create an acetic acid-laden
micro-environment where lead artifacts will corrode even without being in physical contact with the wood."