As far as I am aware, KDE uses it's own internal methods. It is probably correct that one should not try to calculate the size of the dynamic file systems the kernel provides (such as /sys, /proc, etc)

dont know... nevertheless it is not so critical issue...

Have you filed a bug report about this problem? I'm asking because I couldn't find one with a quick search. If you have reported this issue, please provide a link to the report here. Thanks.

yes i filed... minute i will find

heeeey, what is happened, it doesnt exist...
i will fil again...

https://bugs.kde.org/show_bug.cgi?id=298133