Gentoo xpra ebuild - missing dependency on dev-python/cython

[Stroller]

$ sudo emerge xpra
Password:
Calculating dependencies... done!

>>> Verifying ebuild manifests

>>> Emerging (1 of 1) net-misc/xpra-0.0.7.17 from unknown repo
 * xpra-0.0.7.17.tar.bz2 RMD160 SHA1 SHA256 size ;-) ...                 [ ok ]
 * Package:    net-misc/xpra-0.0.7.17
 * USE:  elibc_glibc kernel_linux server ssh userland_GNU x86
>>> Unpacking source...
>>> Unpacking xpra-0.0.7.17.tar.bz2 to /var/tmp/portage/net-misc/xpra-0.0.7.17/work
>>> Source unpacked in /var/tmp/portage/net-misc/xpra-0.0.7.17/work
>>> Compiling source in /var/tmp/portage/net-misc/xpra-0.0.7.17/work/xpra-0.0.7.17 ...
 * Building of net-misc/xpra-0.0.7.17 with CPython 2.6...
python2.6 setup.py build -b build-2.6
Traceback (most recent call last):
  File "setup.py", line 40, in <module>
    from Cython.Distutils import build_ext
ImportError: No module named Cython.Distutils
 * ERROR: net-misc/xpra-0.0.7.17 failed:
 *   Building failed with CPython 2.6 in distutils_building() function
 *
 * Call stack:
 *     ebuild.sh, line   56:  Called src_compile
 *   environment, line 4850:  Called distutils_src_compile
 *   environment, line 1258:  Called python_execute_function 'distutils_building'
 *   environment, line 3466:  Called die
 * The specific snippet of code:
 *                       die "${failure_message}";
 *
 * If you need support, post the output of 'emerge --info =net-misc/xpra-0.0.7.17',
 * the complete build log and the output of 'emerge -pqv =net-misc/xpra-0.0.7.17'.
 * This ebuild is from an overlay: '/usr/local/portage/'
 * The complete build log is located at '/var/tmp/portage/net-misc/xpra-0.0.7.17/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/net-misc/xpra-0.0.7.17/temp/environment'.
 * S: '/var/tmp/portage/net-misc/xpra-0.0.7.17/work/xpra-0.0.7.17'

>>> Failed to emerge net-misc/xpra-0.0.7.17, Log file:

>>>  '/var/tmp/portage/net-misc/xpra-0.0.7.17/temp/build.log'
$

Resolved with emerge -1 dev-python/cython-0.13

Not sure if this is a runtime or buildtime-only dep.