Virtual Keyfigures and Result Row

Hello - We have implemented Virtual keyfigures for below calculation.

If Expected Delivery date on a purchase order is less than system date then Virtual kf1 = 1

Virtaul KF2 = System date - Expected Delivery Date.

This is for Delivery performance metrics.

The problem I am having is when the report is summarized to a material/plant or vendor level the result row sum is displayed wrong. If I bring in more char at the lowest level ie purchase doc no and item..then the count for virtual keyfigures is correct. Did anyone face this issue...how does virtual kfs behave with result rows.

Also when we have virtual keyfigures in a cube...can the query utilize Cache.

Thanks for your replies.