an OSD window, for example the one showing keyboard layout switch may get focus if kwin is configured to focus under mouse. it probably may also get focus if you click on it, not tested.
example OSD window: http://img.5cm.ru/view/i4/yAuK.png

this is a problem , because if the focus switch happens which user types, the typed text starts goind to OSD, not to the window user typed initialy to, which is not the expected behaivour.

Reproducible: Always

Steps to Reproduce:
1.configure kwin to focus windows directly under the mouse pointer
2.configure >1 keyboard layout
3.open a program, allowing you to type anything in a text field, like Kate
4.place you mouse in the area, where OSD appears, usually center of the screen
5.type some text, switch layout using keyboard shortcut and type some text again shortly after the switch

Actual Results:  
only the first part of the typed text appears in the text area

Expected Results:  
all of the typed text should appear in the text area

this happens not only when kwin is configured to focus under the mouse, it's just easier to reproduce it this way. if you set to focus under mouse with a delay you still may get a problem, when you switch to a window, where you want to type text and instantly switch a layout.
user should also be able to click "through" osd, because preventing user from clicking for a ~3 perion from a certain area of the screen, covered by osd is strange.