Could you clarify which version you're using? Our site is running 1.4 and it doesn't do this.
The code that sends the mail is here:
/UserControls/Back/_OrderDetails.aspx.vb
The actual line that sends the email is this one:
SendEmail(strEmailFrom, strEmailTo, strSubjectLine, strEmailText)
If you comment that out, it should prevent mail being sent regardless of anything else.