Package re-use in deployment diagram

[Gordon_Murray]

I have a package (for a server standard build) that I am using regularly throughout a my project.

such that :-
standard build (parent package)
    >>database server (my standard build package)

When the "database server" package is dragged (from the navigator) onto a diagram that exists in a different package (say "DMZ") it creates a reference fine (no problems) but when I drag the same package again it appears to have worked until you leave and return and it has removed all but one instance.

I have managed to get around this until now by keeping the "standard build" package under my "DMZ" package and going through the same motions works fine time.

How can I reuse a package in "sister" branches of the package it was created in?