Hi Bløj,
You haven’t given your custom layout a custom name!
You have changed the file name, but not the name that is read by OS X. For the Mac, the name is still "Dutch".
How to change the name that’s stored inside the keyboard layout (and which will show up on the Mac’s menu bar later on):
In Ukelele, open your custom layout, go to menu "Keyboard", click on option "Set Keyboard name and script…" and type the name you want to show up.
While you are there, also make the script "Unicode", not "Roman".
If you can’t find this in 10.6.8, let me know, so I can have a look on my older Mac how exactly things work there.
In the worst case, I can rename the layout you uploaded and post it back to you.