User could able to initiate the approval twice

Summary

User could able to initiate the approval twice

Content

Hi Wizards,

We have scheduled the program Initiate Invoice Approval Workflow on a daily basis and I could see the approval got trigerred succesfully. 

There is a case, where the invoice is trigerred for approval by the abovesaid program and user again initiated approval for the same invoice manually. 

I believe, once the approval is trigerred by the program, system shouldn't allow user to initiate approval manually i.e. Manage Invoice - Query the Invoice - Actions - Approval - Initiate.

Did someone encounter the issue.  

Please share your thoughts.