Description of problem:
- Imagine there are two process definitions, (1) ParentCallerProcess.bpmn2 and (2) EmbeddedSubProcessTest.bpmn2 .
- The "ParentCallerProcess" contains the following flow:
~~~
Start -> ReUsableSubProcess [calledElement: project1.EmbeddedSubProcessTest] -> End
~~~
- Now the other "EmbeddedSubProcessTest" has the following process flow where the Embedded Sub-Process contains a User Task, and a Throw Intermediate Signal Event , and at the boundary of this Embedded Sub-Process I am catching the signal thrown from the internal signal event.
~~~
 Start -> [ Embedded Sub-Process ](boundary, Catch Intermediate Signal Event, signal ref: SignalOne) -> End
~~~
- This is how the internal flow of the Embedded Sub-Process looks like.
~~~
       Start -> User Task [name: UserOne] -> [Throw Intermediate Signal Event, signal ref: SignalOne ] -> End
~~~

Now, it has been observed that if multiple process instances are started for "ParentCallerProcess" , and we choose "cancelActivity" property of the boundary catch event to "true" , then in this kind of process flow a signal triggered for a boundary catch event on a single instance of embedded sub-process signals other instances too. i.e. after starting two process instances of ParentCallerProcess or EmbeddedSubProcessTest , we can see two tasks are created. However, if we complete just one task the other one suddenly vanishes from the task menu.

- Note, that if there is no "ParentCallerProcess" created in the KJar, i.e. there is no one to call the EmbeddedSubProcessTest process within the same runtime, this issue does not occur.

- For this specific use case we have used Singleton ksession strategy, but even while building the Business Central project using Request strategy too the same issue can be observed.

[WORKAROUND] As per my observation, this issue does not occur if the "cancelActivity" property of the boundary catch event in the process EmbeddedSubProcessTest was set to "true". If we put it to "false" then this issue does not occur.

Version-Release number of selected component (if applicable):
- jBPM 6.0.x

How reproducible:
- Use the attached "CancelActivity_Bug_BoundaryEvent_repo.zip" bare repository or the pre-built kjar from my Business Central project "backup_repo.zip" to replicate the issue.

Steps to Reproduce:
1. Extract the contents (.niogit folder) from the "CancelActivity_Bug_BoundaryEvent_repo.zip"  archive and place it under "jboss-eap-6.1/bin/" location of BPMS 6.0.3 installation. Optionally you can use the pre built KJar packaged inside "backup_repo.zip" archive to import into the artifact repository through Business Central.
2. Build the project which has the following G.A.V. details "org.kie.example:project1:2.0.0-SNAPSHOT" . If the KJar archived in "backup_repo.zip" file is imported as artifact , then you need to deploy it as a New Deployment Unit, and you can choose Singleton or Request strategy.
3. Start two process instances from any of the process definitions available in Business Central.
4. Make sure you have a user login for "annguyen" in Business Central , and once logged it with this user two tasks for UserOne is available. Try to complete any of them.

Actual results:
- Both the task vanishes from Task list if you just complete one of them.

Expected results:
- One one of the tasks should be completed.

Additional info:
- Please also try the workaround by setting "cancelActivity" to "true" for the boundary event in the embedded subprocess.