See the information provided on this web site:
Summary
If you use Update Manager to upgrade your packages, and it
offers to do a Partial Upgrade do not accept it without thoroughly
checking what packages it offers to remove, upgrade and install. If
you do, you will most likely end up removing packages that shouldn't
be removed, and waste time and effort repairing your testing
installation and asking for assistance.
Most Partial Upgrade situations occur due to package archive
inconsistencies, which will typically be resolved within a few hours.
If your package manager is confused, and so are you, simply wait and
hold off the updates until things settle down.
Short Version
Due to the fact that uploads to the repositories of the
active development branch are asynchronous and uncoordinated,
dependencies of certain packages may arrive later than the dependent
package. This causes package management tools such as Update Manager,
which are mainly meant to be used with stable releases of Ubuntu where
the package archive is always consistent, to interpret the situation
as requiring a dist-upgrade to install new packages and/or repair
packages in a reqreinst (requires reinstallation) state. What Update
Manager performs when doing a "Partial Upgrade" is a dist-upgrade.
When testing development releases, most of the time, a Partial Upgrade
is undesired. The situations where it's needed are limited to new
packages obsoleting old ones (as in the case of the software-center
package replacing software-store) and package removals from the
archive.
Do not assume that since you're running a development release, a
Partial Upgrade is necessarily warranted.