Opeartion ADDDB - how does it work?

We have a bit of a weird problem with an employee - in essence he is getting the wrong overtime.

On investigation it seems that the our Time Type Z060 has a value in it, when it shouldn't.

There is a statement "ACTIO Z533" in our Time Schema which appears to zeroise the Time Type Z060 - the code is:

Rule GrRule TType VaKey Operation

Z533 * **** HRS=S Set

Z533 * **** ADDDBZ062Z Set day balance = 0

Z533 * **** HRS=S Set

Z533 * **** HRS-DZ015 Subtraction

Z533 * **** ADDDBZ060Z Set day balance = 0

Z533 * **** ADDDBZ061Z Set day balance = 0

The second line from the bottom is, I think, the line that zeroises the Time Type Z060. However, immediately after this code in the schema is a print of the values in the Time Types:

TimeType Name Number

Z070 Claimed Overtime 8.7000

Z062 WS Hours 7.0000

Z060 Hours Worked PT Overtime 7.0000

Z061 Hours Worked FT Absence 7.0000

Which shows that Time Type Z060 has a value of 7 hours!

How can this be? If it was zeroised immediately prior to the print. Has any-one come across a similar problem?

Any hints/tips gratefully received.