I'm not sure if this is a bug or not, but I'm using the Relation module and I'm trying to set a rule that updates a Relation's Endpoint's fields when that Relation is updated. For example:

Member A has a field status "available"
Member A has been connected to Relation A
Member A has it's status field changed to "unavailable"

I can use rules to assign the following events, conditions and actions:

Event: Relation has been updated

Conditions1: Entity has type (relation:endpoints:0, contact)
Conditions2: Entity has field (relation:endpoints:0, employment_status)

Action: Set a Data Value (employment_status, "unavailable")

This causes these errors and I haven't found a way to fix them yet:

Notice: Undefined property: stdClass::$revision_id in drupal_write_record() (line 7030 of ...\www\includes\common.inc).
Notice: Undefined property: RedhenContact::$revision_id in EntityAPIController->saveRevision() (line 525 of ...\www\sites\all\modules\entity\includes\entity.controller.inc).
Notice: Undefined index: revision_id in EntityAPIController->saveRevision() (line 528 of ...\www\sites\all\modules\entity\includes\entity.controller.inc).
Notice: Undefined index: revision_id in EntityAPIController->saveRevision() (line 533 of ...\www\sites\all\modules\entity\includes\entity.controller.inc).
DatabaseTransactionNoActiveException: in DatabaseConnection->rollback() (line 1024 of ...\www\includes\database\database.inc).

I'm hoping I'm not chasing my tail on this, and that there is another way to do this in Rules.