-Djava.library.path always overwritten with some default

in the launch configuration for my configured jboss server i need to add another directory to the parameter -Djava.library.path.
after editing it looks like
-Djava.library.path="/home/arne/jboss-4.2.2.GA/bin/native:/foo/bar/"
saving and reopening shows instead
-Djava.library.path="/home/arne/jboss-4.2.2.GA/bin/native"

adding another parameter instead
-Djava.library.path="/foo/bar"
resulting in
-Djava.library.path="/home/arne/jboss-4.2.2.GA/bin/native"
-Djava.library.path="/foo/bar"

ends up with
-Djava.library.path="/home/arne/jboss-4.2.2.GA/bin/native"
-Djava.library.path="/home/arne/jboss-4.2.2.GA/bin/native"
after saving

obviously some simple logic checks for the existence of the -Djava.library.path parameter and overwrites it with a default instead of at least appending its default.
i don't really see what's the meaning behind that, and therefore am convinced it has to be a bug.
additionally, it stops me from running at least one webapp, that requires the parameter to be set correctly.