Labor Correction for Construction Company

We are a construction company and have recently converted to Oracle. Our Field Timecards are charged to jobs. The employee master is set to pull from the payroll constant on the job master.  

Sometimes we have to move labor from one job to another. For example a truck allowance is charged to one job and should have been charged to another. We have been doing some testing in a test enviorment and tried to key the negative PDBA with a lum sum of $1000 and a positive lum sum with the same PDBA of a $1000 so the gross difference is zero and would just correct the taxes and burden following the labor to hit the correct job. Upon testing we noticed the tax areas don't seem to recognize the negative amount.