There is a nasty bug in PeopleSoft CRM 9.1 that can lead to case data being overwritten by data from another case.
Just open two different cases from the My Cases pagelet. Each opens in a new window but they have identical URLs apart from the CASE_ID. The effect of this is that changes made to one case result in the component globals such as CASE_ID being overwritten on the second tab. If that tab is then saved, then incorrect data is written back to the database. Insidious little bug.