Why does Standard reorg change "not null" behavior after rerog?
When Revalidate originally validated constraints is not selected, the ENABLE VALIDATE state is not preserved in most cases, but constraint creation is faster. This is because data is not checked for compliance with ENABLE NOVALIDATE constraints. However, a check is not needed as data was checked prior to reorg.
After originally validated constraints are recreated enable novalidate, key columns are shown as NULLABLE in DESC results. This is the case even if the columns have a constraint and were shown as NOT NULL prior to reorg. However, the nullability state of the columns is preserved.
You can avoid this by selecting Revalidate originally validated constraints in scripting options.