Hello, I don't really know where to put this. I have just upgraded to KDE SC 4.11 and now are my special mouse buttons >3 'dead' (but scrolling works). I'm using xbindkeys to map two mouse buttons to Kwin actions but now xbindkeys can't anymore recognize the buttons. Try it: "xbindkeys - k" (opens a test window for input). In KDE Plasma 4.11, I can press the two extra mouse buttons and nothing happens.
"xev" is also deaf on these mouse buttons.  This comes when I press B9.:
---
EnterNotify event, serial 40, synthetic NO, window 0x6200001,
    root 0xbb, subw 0x0, time 840276, (7,173), root:(2320,1385),
    mode NotifyUngrab, detail NotifyAncestor, same_screen YES,
    focus YES, state 0

KeymapNotify event, serial 40, synthetic NO, window 0x0,
    keys:  4294967227 0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0 
---
BUT it works just fine in TWM:
xev:
---
ButtonPress event, serial 29, synthetic NO, window 0x1e00001,
    root 0xbb, subw 0x0, time 187573, (121,176), root:(752,962),
    state 0x0, button 9, same_screen YES
---
And xbindkeys -k in TWM:
---
Press combination of keys or/and click under the window.
You can use one of the two lines after "NoCommand"
in $HOME/.xbindkeysrc to bind a key.
"(Scheme function)"
    m:0x0 + b:9   (mouse)
---

My first attempt was the Arch Linux forum but no one could help me there. I think it is a bug.

Reproducible: Always

Steps to Reproduce:
1. Try a special mouse button outside of KDE with xev
2. Press special mouse button in KDE with xev
3. xev cannot recognize the button running in KDE.