Comment 48 for bug 1509139

FYI, I made this work in Linux Mint 18 KDE by replacing the following line in /usr/bin/xdg-mime

 1000 # KTRADER=`which ktraderclient${KDE_SESSION_VERSION} 2> /dev/null`
 1001 KTRADER=`which ktraderclient 2> /dev/null`

It likely has to do with Plasma 5 and some greps.

 $ ktraderclient5 -v
ktraderclient 5.6.5

 $ ktraderclient -v
Qt: 4.8.7
KDE Development Platform: 4.14.16
KTraderClient: 0.0

Chromimum was able to set itself default after the change, and wont complain any more.

I see open Bug ref. with xdg-utils: https://bugs.freedesktop.org/show_bug.cgi?id=98562 (hopefully they'll fix this for good some time)