Excel processes lingering

I have been succesfully using jawin for over a month, automating
PowerPoint, Word and Excel, happily reading and exporting content from my
java application.
The one matter that puzzles me right now, is the fact that, after using my
application a number of times, I consistently find Excel processes alive in
the background. Those processes are not visible in the task bar, by they do
show under task manager/processes.
I do the same set of actions (or their equivalent) for all three
applications, but only Excel kind of stays alive, clogging my system with
unlimited instances of itself.
I was wondering if anyone in this list has experienced a similar behavior?

(I am running Office 2003 on Windows Server 2003.)

 Reuben