Hhm, I may tell only about two cases in my practice:
1). Direct deletion data from the SEM-BCS cube - by different means, from BW, BPS, BI-IP etc. The system does not delete the record, but posts another record with the inverted sign for amount (storno). Depending on the set of parameters in the selection screen (and the set of infoobjects in the cube), the system may show these two inverting records separately or just collapse them, showing nothing.
2). The standard inverting of documents in SEM-BCS.
If you wood provide more details, probably some another thoughts could came into mind.