Created attachment 293103 [details] log of failed compilation net-ftp/proftpd fails to build due to sandbox violation (I'll attach logs and proposed fix). Tested and happens with net-ftp/proftpd-1.3.4a and net-ftp/proftpd-1.3.4_rc3 on amd64 when kerberos is in USE for this package, rpm binary is installed and probably when directory /var/lib/rpm exists (it could happen if the directory/files in it don't exist too, haven't tested). Interestingly I was able to confirm it on amd64 only.
Created attachment 293105 [details, diff] a simple tested patch for 1.3.4a (ebuild)
Created attachment 293107 [details, diff] a patch to be used in ${FILESDIR}
Thanks a lot for your report! The next ProFTPD 1.3.4* commit will include a fix for this issue which is based on your proposed patch!
Indeed thanks for your report! Fixed with proftpd-1.3.4a-r1 by Bernd, now in CVS
Nice job, glad to see it fixed.