Version: (using Devel) The taskmanager is a stubbern plasmoid. If you have it outside of your panel, just floating on your desktop, it will try to 'correct' your scaling attempts, most of the time incorrect. Even worse; quitting and restarting plasma sometimes makes the taskmanager looks horribly small. General rule; it keeps on getting smaller, no matter how hard you try to get it to be a nice big taskbar. To reproduce, insert a taskmanager plasmoid somewhere on your desktop (i.e. not on a panel). It defaults to a horizontal on. Some 300x80 pixels or so. Try to scale it so it becomes a vertical taskmanager. With that I mean a taskmanager that is 250 pixels wide and 1000 pixels tall. Using the controls, I found that it basically can't be done. (even while holding the ctrl or shift buttons).
Generalising, it's now just broken when not on any panel.
taskbar has changed a lot since the report, by the way doesn't try anymore to resize itself