Do a Payroll Simulation for that employee, with the "Display log" box checked, and drill down into the log until you find Function P0015.
Double-clic on that Function and look how the WT from IT0015 is being processed. Does it's value in the Output correspond to it's value in the Results Table? If not, then you must find where the additional processing takes place (in which pcr).
As for the "Exemption limit", is that something related to the employee's Country of work or Country of residence? Where is that limit set/identified?