Am having a recurring problem in that when I invoice a project the project remains amongst all other active projects within the projects list. Usually once I have invoiced the project is complete.

I would suggest is that their be a popup window with option to mark project status as complete or not IF all slips are marked as done and the user clicks to invoice the project.

Let me know what you think?

You can achieve your desired result by changing the Bill time in: x minute increments under the General section in the Preferences.