At the moment it's disabled by default, yet you can set it in a corner. Then it won't work until you enable the effect on the kcm. This doesn't seem very intuitive and I'm sure it will make some users think it's not working. I'd recommend enabling whatever effects are selected for an edge automatically. I can imagine that disabling back is a bit more complex but at least it won't behave unexpectedly.
*** This bug has been marked as a duplicate of bug 448568 ***