Workflow Modeler Problem

cc96ai

we are using workflow modeler,
we got some weird situation.

[Start]->[External task] -> [Opendeploy] -> [CGI Task] -> .....

in normal situation, once the user click on [submit] in workflow windows, it suppose close immediately, (it did sometimes)
However, sometimes it will go to CGI task.
I have no idea why this happened

I checked the [modelinstance] directory, those genearted ipm, it is same.
where else can I look for this issue ?

Thanks