Hello:
The first step in your investigation is to look at the characteristics of the batch(es). Which batch did those reversed transactions belong to? What about the original transactions - same batch or different? What posting sequence(s)?

Then go to Inquiries | View Batch Status. Add columns to display "Auto-reverse", "Ledger", "Date created", "Date last edited" and "Last edited by user". What does that tell you about the batch(es) in question? If Auto-reverse = "Yes" and Ledger = "IC", then take a copy of the client's data and see if you can reproduce that circumstance. Ask them what procedures they follow.