Hmm, it does sound to me like a race condition caused by the -j3 in the 'make install' step. Most people wouldn't use -j3 for that, I suspect
, but yours is presumably hard-wired into your environment.
I don't know if the -j3 can be overridden like this, but try:
make -j1 DESTDIR=$pkgdir install
Or perhaps you know some better, arch-specific way...