Workflows getting triggered automatically by system

Hi Experts,

We have a customized workflow which is triggered using a custom program (Custom Event).

From last 3 days system is triggering the workflow automatically

and the workflow is triggered every half an hour from 12 AM till 9 AM only.

These workflow instances are for the same business object key value.

On last Thursday at around 5 PM, workflow was launched manually by a user

and from friday midnight system is trying to launch the workflow automatically for the same Business Object Key value.

When i saw the logs of the workflow triggered manually by user,

there is a comment that 'Start Event Received',

But in the logs related to all other workflow instances which are created autoatically by the system,

there is no comment that ' Start Event Received' .

Please advice, these workflow instances should not be triggered automatically.

Version: ECC 5.0

Regards,

Vargi