Activities could read from the ZODB an state older than the one
that caused the activity to be created, if:
1.Zope client node (node A) processing an activity  message is different
  than the one that created the activity (node B),
2.The object cache for node A contains objects concerning the activity
  message (or its container)
3.The node A hasn't yet received the invalidation message from the ZEO
  server, for instance, if its still on the network layer (kernel buffers,
  routers in between, etc...)

The simplest fix for this issue is sending a synchronous message to the
ZEO server before the beginning of a transaction. This message will act
like a “network barrier”, making sure that any invalidation messages
sent before that point from the ZEO server are already received, and the
transaction can begin with an “updated enough” state.

Additional note from Yoshinori : This patch must be proposed to zope
developpers as soon as possible and see with them if this way is the
best.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@39710 20353a03-c40f-0410-a6d1-a30d3c3de9de