I can verify that installing libatk1.0-dev and gobject-introspection-repository into a karmic system, and upgrading libatk1.0-dev to the package version found in lucid, that package installation fails. I can also verify that once lucid-proposed was added to sources.list, the upgrade to the package version in lucid-proposed succeeds, with libatk1.0-dev successfully replacing gobject-introspection-repository.
I can verify that installing libatk1.0-dev and gobject- introspection- repository into a karmic system, and upgrading libatk1.0-dev to the package version found in lucid, that package installation fails. I can also verify that once lucid-proposed was added to sources.list, the upgrade to the package version in lucid-proposed succeeds, with libatk1.0-dev successfully replacing gobject- introspection- repository.