Unit Price not calculating correctly on split lines when the date is changed.

We are using Advanced Pricing and have a volume adjustment based on quantity ordered.  If the line is split during commitments to multiple lot number, the price calculates correctly based on the original order quantity.  However, if we have to change the scheduled pick date the price then does not calculate correctly - the price calculates based on the split line quantity.  We are also not able to manually allocate lots to split lines as the price will not calculate correctly.