Ubuntu (or maybe this comes from Debian) has the most backward, annoying, exasperating package management, in my opinion. Imagine the following:
apt-get update
[...]
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
42 packages can be upgraded. Run 'apt list --upgradable' to see them.
Then we run upgrades:
apt-get upgrade -y
[...]
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following upgrades have been deferred due to phasing:
[ list of all 42 packages mentioned on the update ]
And, of course, Landscape will report all those machines with phasing packages as having “package upgrades available” and, often, as having “security upgrades available”, but there are none—or nothing can be done about it, “due to phasing”.