A first workaround will be to add:
skinparam wrapWidth 100
With that we can observed the expected result:
If that can help,Regards,Th.
Thanks a lot for your quick help.
It works well as far as I am using normal characters.
I also found that it doesn't work well when it is used with Japanese characters.
Maybe this is seen only in my special environment (= Japanese environment).
For that you could add some secable/breakable places, as space...