If you install some rpm without yum (
rpm -Uvh), you should see the following error:
... Transaction Test Succeeded Running Transaction Warning: RPMDB altered outside of yum. Installing : whatever.x86_64 ...
This is because the yum database (
/var/lib/yum/*) is out of sync with the rpm database (
/var/lib/rpm/*), and to fix it you can execute:
yum history new
You can also wait to install another package, then yum will resync the databases