Check Sent out. Of course I am not on stock but with kp52, bb-power, gnu-tar and all other devel stuff! After investigating with 7z I am not any point further. The zipped part of control.tar.gz and also data.tar.gz looks okay (when extracted it is a valid zip file). And removing those parts from fkdep.deb will also bring a valid zip.
printf '%-16s%-12s0 0 100644 %-10s`\n' $1 $timestamp $size >> $deb