Quote Originally Posted by ibates View Post
Unfortunately, the installed apps were not listed in either Synaptic or Ubuntu Software Centre.

However, all is now solved, thank you all. Installing Gdebi Installer fixed the problem, and all I had to do was install that app and reinstall the apps and vilola! There they all were.
The packages were probably not installed correctly or completely the first time. (This -- "...which is not available through either Synaptic or the Ubuntu Software Centre, but which was nonetheless installed using the Ubuntu Software Centr.." -- suggests it was a package from somewhere other than the Ubuntu repos, which opens, at least, the possibility of a fault in the package.