Sporadic class cast exception during stateful session updating

We sometimes encounter the following exception during update of stateful session:

org.drools.core.reteoo.RightTupleImpl cannot be cast to class org.drools.core.reteoo.LeftTuple

Up until now, we were not able to consistently reproduce the issue. Following the same steps after creating the session did not necessarily result in the exception, but we had some progress lately and the attached project triggers the exception every time.

Project consists of multiple classes used when inserting facts and two variations of rules in separate .drl files.

Short test description:

• Create a stateful session with rules from initial.drl
• Inserts several facts
• Update container by altering between rules from initial.drl and modified.drl