I downloaded the source to the (video editing) application "kdenlive" (version 0.9 just released), and following the instructions on the kdenlive web site, compiled it, and installed it on my Linux Mageia Cauldron laptop. Maybe I did something wrong, maybe not. Anyway, disaster ensued.
Whenever I launched an app from the panel or the KMenu, I would get an error about missing mimetypes. Logging-out and logging back into KDE didn't help, and popped up a window error dialog listing dozens of applications with missing mime types. Rebooting the system didn't help.
In short, the only way to launch an app was with Alt-F2, or from the command line.
Thrashing around online brought forth few references to this issue, but I did find a brief mention about kdelibs4 and mime types.
So, in desperation, I reinstalled "kdelibs4-core". Under Mandriva/Mageia this can be done from the command line using the "urpmi" utility. To do this, become the root user with su. Then enter:
urpmi --replacepkgs kdelibs4-core
Fortunately this brought my system back to normal. Problem solved.