Item costing on production output

We are using NAV 5.0 production orders with FAMILIES.

All finished / output items are standard costing with manual flushing - we only determine the combinations of what we are going to produce based on the actual output.

All raw material / consumption items are standard costing with manual flushing using the expected quantities - we post output before we post consumption.

When the output journal is posted, based on the actual quantities, the cost variances are calculated and the adjust cost item entries correctly calculates the variances and post these to the variance account. BUT, for some reason, on certain output items, the actual cost is calculated and the FULL amount is posted to the variance account:

Direct Cost  line >Expected 18 844  >Actual 17084 (the amount which I would expect to post to variance is 1760, but the amount which does post to variance is 17084 - the actual amount.)

The valued quantities for both the direct cost and variance lines are the same, 1095;

The invoiced quantity (output) and valued quantity are the same, 1095

This does not happen consistently with the same item from the same family on every production order.

We have set our adjust cost to run automatically and once a month we run it as part of our month-end routine.

I have tried to replicate this in a test scenario, but the variance which is posted is the difference between the expected and the actual.

Can anyone give me an idea why the FULL ACTUAL amount is posting as a variance?

Thanking you in advance.