Bug 369568

My OS : MAUI 1 (KDE Plasma 5.7.5 - 64 bit)
During the file transfer (cut and past 40-50 jpg pictures from one folder to an other in the internal hard disk) with one dolphin window opened, I noticed that the panel was entirely "frozen" (clicking with the mouse on to the panel icons/application starters : menu icon / firefox icon etc.- it did nothing !!), until I could see a (plasma) message that the transportation of the files was done!! The problem occurs every time ! 
During some other file management jobs (plenty of files) the system load is very high, especially if dolphin remains open. Somehow and sometimes my PC reminds me a Sinclair Spectrum I had 30 years ago..... The user has to wait making a cigarette and there is no multitasking. I think that, somewhere between dolphin and plasma is possibly hiding a bad management of available CPU resources !
I say that , because closing dolphin immediately after the file management job starts (file removal - tag changing - etc..), it seems that the work is completed normally and much faster (in background) while, the user has the ability to do something else in foreground. 
I have installed the MAUI OS in a SSD (it's a new Samsung SSD 840 - it seems good and fast).
I keep some files here but I also keep files in an other disk (hdd - ext4 format).
AHCI mode is enabled (BIOS) for all the SATA controllers . I think there is no problem with the disks.
MY PC : Mother board / Gigabyte GA-X38-DS5 , CPU / 2 x Intel Core 2 Duo E 8400 3.00 GHz , RAM 8GB , Graphics / NVIDIA Geforce GT 710

Reproducible: Always

Steps to Reproduce:
1. Cut and past 100 or more icon files (jpg - etc) from one folder to an other or try to give a new common tag to many files together in the same folder. Keep Dolphin open.
2. Try to click on the menu icon before you see the report that the file management job is done.
3.