Another RLM issue - dropping Lines

During the past couple weeks we've had occurance of SO Lines dropping without any rhyme or reason.  Ironically, it started happening after I changed the Processing Rule - In Transit, from Shipped Lines to Match on Partially Shipped Lines.  For example, a firm demand line kept coming in weekly for a 20-April-2012 request date.  Then on 09-Apr a new 830 schedule for this item came in with 1 Past Due Firm Demand Line with a qty of 0, then next line was for 48 for 20-April.  The DP ran and dropped this line with the warning: Warning :: The schedule line qty 48 for ship from-ship to-customer item ARC-CASE-OEM-GI-87356887 on request date 20-APR-12 (Original Customer Request Date 20-APR-12) will be updated to zero after reconciliation (Schedule Line 2). The corresponding order 101942 line 18.1 will be dropped. Additional Matching Attribute(s)