Created attachment 103887 [details] screenshot of ksysguard Plasmashell takes 150% while copying multiple small files on samba share that was mounted to the filesystem. Didn't check if that happens when moving local files.
There are several bugs flying around here in the bugtracker concerning this bug and I do not think you provided enough information to further investigate where the problem may lie.
*** This bug has been marked as a duplicate of bug 378010 ***