[blocks B     ] >=x11-proto/xproto-7.0.6 (is blocking x11-libs/libX11-1.0.1-r1)
...
<snip>
...
[ebuild     UD]         x11-libs/libX11-1.0.1-r1 [1.0.2] USE="ipv6 -debug" 0 kB 
[nomerge      ]          x11-libs/libXau-1.0.1  USE="-debug" 
[ebuild     UD]           x11-proto/xproto-7.0.5 [7.0.7] USE="-debug" 0 kB 

(Workaround: emerge -1 xproto)