It sounds to me as a difference between OS installs of Glassfish. Maybe you should take your problem to the Glassfish forums (or whatever they have, I'm not familiar). Not trying to be rude, I just think they might be more able to help. This is not a SEAM issue.
BTW, your English is better than modern youth's Dutch here :P
I understand what you say, and I agree - the reason I haven't brought this up at the Glassfish forum yet is that I was hoping it was a specific Seam issue. So I posted to see if such a problem was a common one, or a known issue for someone lingering here.
As far as the versions of glassfish are concerned, they are the same build version - only different concerning the OSes at hand. I also suspect that this has something to do with how glassfish searches for files/resources in different OSes...
Another curious thing.
If I run the application through Netbeans (starting glassfish through the IDE and deploying the application through it as well), even on Linux and using the same version of the application server, it all works well.
The problem can only be noticed by using the deploy tool available at the admin console web app.
Very odd indeed. I'm confused :D