Software from Software Center / Third Party typically takes a few seconds to install, but
the blue bar keeps bouncing back and forth
the "Install" button remains on "Install"
... long after the software has installed.
This is pretty bad because it's misleading. On a number of occasions, I've seen people closing down the Software Center and saying like "It takes an eternity to install this", which is in fact not the case at all.
I've experienced this in Solus Plasma. I can't tell whether the other flavors are affected as well or not.