This is an upstream fault, I was in contact with the developer and he issued me this .diff to fix the issue, he was using gentoo as well when I reported the problem directly to him in IRC. Basically if you try to download something off a server which is running pure-ftpd (possibly other servers) it will fail, Only succesfully able to download really small files like ebuilds/md5s etc, anything larger will fail.
Created attachment 100031 [details, diff] multiline-data-command-fix.diff Patch for version net-ftp/kftpgrabber 0.8.0_beta1
Fixed in 0.8.0_beta1-r1 and I regenerated and added a new patch for 0.8.0_alpha2-r1. Fixed in CVS. Thanks for reporting the issue so quickly.