Is WSA scope unique for each employee in the pay calc?

Summary:

Are WSA variables always absolutely uniquely scoped to each employee in a pay calculation?

Content (please ensure you mask any confidential information):

I just had a weird problem - using WSA in fast formulas to track values between assignment and payroll relationship level elements. Basically to add up salary across multiple assignments and have a total salary figure available for a payroll relationship level voluntary deduction. Much neater than using balances.

The WSA name was just 'total_tracked_salary', I didn't add any IDs to it because I thought the value would be unique to each employee.

It worked perfectly when calculating employees using quickpay, but in a full payroll run with many employees I was getting extremely high nonsense values (in the millions) when retrieving the WSA.