WorkFlow Filtering

Hi Guys. 

Hoping someone can help. 

I have a Workflow that i am trying to only execute if a VA is set to TRUE. at the moment the Workflow will kick in anytime there is a change to the VA. 

Operation that starts this workflow: Modify Properties

Target object type: User

Workflow start upon a request to changes to: This is my VA and lets call it VA1

Initiator Any User

Container  Active Directory but will dial this down a bit.   

Now under thee filtering no matter what i set to VA1 to only run if the value is true , it seems to run for both TRUE , False and Clear. 

Any ideas?