I have just upgraded to Linux Mint 17.1 Cinnamon 64bit.

For various reasons, I did a complete format and install, so the following may not affect those just doing an upgrade.

There is a small problem with running some KDE applications.  As an example, I installed KNetWalk [a small timewaster!] and this is the menu bar that is displayed –

With a bit of research, I found the answer as submitted by Clem.

sudo apt install kdelibs-bin kdelibs5-data kdelibs5-plugins

To install the icons –

sudo apt-get install oxygen-icon-theme*

Rerunning the application, this is the result –

Just in case anyone has similar problems…….