InfoPath Dev

I have a InfoPath 2007 Form and the code behind for the form is C#.

When two or more Infopath forms are being  opened in the same window using the same form template, submission of one will close the others without submitting them. This problem only happen occasionally not always.

I checked my code, I think the problem might caused by the code below but I'm not 100% sure since this problem only happen occasionally:

 this.Application.ActiveWindow.Close(true);