Hi Marc,
You have a defaulting calculation here. Assuming you have selected both stored and calculated checkboxes for this KF1 in configuration, the defaulting expression gets auto generated when you activate the model. However for this to happen, as mentioned in model reference guide, the stored input KFs that go into the calculation chain should have the same base planning level as KF1.
In your case, if KFINIT (calculated KF) is calculated based on stored KFs in its calculation chain at PERPROD level, then the system on activation correctly puts the disaggregtion expression.
If KFINIT has other planning levels eg KFINIT@PERPRD = SUM(KF2@PERPRODCUST) , then this will not work for diaggregation expression as it is based on calcualted KF at different plan level. So for this you need to use a Copy Operator to store KFINIT to KFINITSTORED and use in disagg expression. Other alternative is use ADVSIM operator but not recommended if you can do with Copy operator,
Hope this helps.
Thanks,
Raghav