hello, i wonder why not every application icons are changed when i change icon theme? I mean that in start menu the icon of e.g. smplayer or qmmp is changed but when I run it, I see another old icon at the panel, and I'm unable to change it? is that normal behavior of panel?

The icon set in the Task Manager is provided by the application directly. Some applications have these icons compiled into them, so they cannot be changed. KDE applications generally source theirs directly from the theme which is why they obey the theme.