Duplicate insert nofifications occurring

We are using the Oracle adapter 4.1.1 SP3 with ADK 421. SP4 and performing an Insert Notification operation on a table. For the past few weeks, we have noticed a strange problem.

Though the record is inserted only once on the buffer table (verified by having a creating temp trigger/table listening to the buffer table and seeing only one record inserted), but somehow the insert notification occurs twice which causes the duplicate of the same record. The adapter is running on a single instance, but when this duplicate triggers occurs, there are two instance of the adapter running (adapter logs from the adapter_trace folder)- which explains the reason for the duplication.

The problem occurs randomly and hence very difficult to simulate also.

Question is: how is the adapter automatically increasing the number of instances and causing this duplication to occur.