When should a package be ubuntu-versioned?

[Mike Bird]

There are packages in the repository with exactly the same names
as Debian packages but with different dependencies.  This is
creating havoc with some of our tools.

What I need to know is whether this is an error for which bug
reports should be filed against the changed Ubuntu packages, or
whether it is permitted in which case we have to make some
changes to our tools.

Example: python-imaging_1.1.5-4_all.deb

Thanks,

--Mike Bird