I suppose it may be related to that magical writing of version or .xml file. Build log attached.
Where is the build log? But it does not happen when manually compiling (on debian though), so it must be a ebuild issue?
Created attachment 462528 [details] media-gfx:darktable-2.2.1:20170204-113436.log.bz2 Sorry, here it is. Bugzie must've rejected it due to uncompressed size ;-f.