Connections to Interbase Server that do not seem to disconnect

I am testing my application built with Delphi 3.0 and Interbase Server
installed on NT server.  After the application is opened and closed on 3
clients, if the application is opened on another client, it runs much more
slowly.  If I shut down one of the first 3 clients and restart the 4th
client computer, then the application runs normally.  Is there a way to
ensure that the database connection ends when the application ends?

Another strange problem is that if I open a certain database many times,
then the server shows that database to have one or more connections even
after I shut down all the clients that ever opened the application!!

Help!