I recently upgraded a Kubuntu 15.10 operating system to Kubuntu 16.04. I used to use single-click to open files and directories in the Dolphin file manager. This stopped working after the upgrade. Only double-click would open files and directories.
$ cat ~/.config/kdeglobals | grep SingleClick SingleClick=true
Further investigation showed that this was a known bug. It is fixed, but I guess it will be a while before that flows downstream to Kubuntu.
The only solution that worked for me was to install the older Dolphin from KDE 4 and running it instead of the default Dolphin from KDE 5:
$ sudo apt install dolphin4 $ dolphin4