Yes, I have the same. The window-manager switches on its own after I 'throughput' a link for
instance a browser in case of feedreading or tabbed mail in the browser.
Only Firefox does not
give the problem. Xfce has quite some settings for the WM (Window manager tweaks), I love it, but I don't see this
kind of setting-tool in KDE 2013.
(I'm experimenting with KDE and it is a beauty really, but not 100% finished in my humble opinion.)
Anybody an idea about this desktop switcher?

(By the way, it would be lovely when the WM in KDE would give more detail like old WM's.
That gives the user a little more help.)