Icons in low resolution in the "task change" (alt+tab) in KDE plasma


some applications icons in the “task change” (alt+tab) are in low resolution: https://s10.postimg.org/qtdx1kfux/icons_low.png

I’m using the mode “big icons” in the “task change configurations” and I’m also using the default breeze icon theme. I’m not sure if the bug is on the icons or in the task manager “type”.

Do you know how can I solve this? Many thanks.