From apt's perspective they are different packages -- each with its own version. "Upgrade" (see apt's man page) *promises* *never* to remove a package. It would have to remove libkpmcore8 to install libkpmcore9.
I understand.I will try to contact the package maintainers and ask them if they couldn't provide a package named "libkpmcore" then and using normal version numbers for this package as usual for other packages.
Thanks a lot! Marco