Counterexample reduction in test/model can generate a malformed workload, which has transaction conflicts that don't exist in the original workload. For example, consider the following example:

create_table(2, "table2", "r", "Q")
begin_transaction(1179)
insert(2, 1179, 8708, 161320)
prepare_transaction(1179, 1440177)
begin_transaction(1201)
insert(2, 1201, 46514, 684979)
remove(2, 1201, 8708)
commit_transaction(1201, 1473940, 0)

Note that transaction 1179 does not have the commit or the rollback operation at the end, which means that the transaction was implicitly rolled back due to the database crash or restart in the workload, which was removed by the counterexample reduction. In this case, this created a new conflict within the workload, which results in a failing workload that's not a consequence of any WT bug.