Following code, with foo having portal type Foo which is
not installed yet (thus it is broken) :
connection = self.getConnection(portal)
foo = connection.importFile(file_obj) => this does a savepoint
foo._p_changed = 1

Then next savepoint was raising :
PicklingError: Can't pickle <class 'erp5.portal_type.Foo'>: it's not the same object as erp5.portal_type.Foo )

This was because we had :
foo.__class__.mro() : (<class 'erp5.portal_type.Foo'>, <class 'ZODB.broken.PersistentBroken'>,
 <class 'ZODB.broken.Broken'>, <type 'persistent.Persistent'>, <class 'erp5.portal_type.Foo'>,
 <class 'Products.ERP5Type.dynamic.lazy_class.GhostBase'>,
 <class 'Products.ERP5Type.dynamic.lazy_class.ERP5BaseBroken'>, <class 'Products.ERP5Type.Base.Base'>, *TAIL)

and

erp5.portal_type.__getattribute__("Foo").mro() :
(<class 'erp5.portal_type.Foo'>, <class 'Products.ERP5Type.dynamic.lazy_class.ERP5BaseBroken'>,
  <class 'ZODB.broken.Broken'>, <class 'Products.ERP5Type.Base.Base'>, *TAIL)

Classes where different because new class with new inheritance was created by
ZODB.serialize.ObjecReader.load_persistent which does :

if issubclass(klass, Broken):
    # We got a broken class. We might need to make it
    # PersistentBroken
    if not issubclass(klass, broken.PersistentBroken):
        klass = broken.persistentBroken(klass)

Since ERP5BaseBroken is patched to mostly be like a PersistentBroken,
make sure we allow serialization to identify ERP5BaseBroken as a
PersistenBroken class.