As reported in bug #418269,
the icon size is only selectable in icon view mode.
but selecting a different icon size on icon view mode also changes
the size of the icons in list view mode.
It is needed a plasmashell restart for them to go back to small (default) size.
This creates a problem since the list icon size is hardcoded by default to small,
but it seems it is being changed on other places of the code.
Upon discussion, there seems to be nothing wrong with having a list mode with difference icon sizes.
( for example i like them a little then small, as to be easier to view and click ).