This tftpboot.img on SPARC, I assume the installer is the same across architectures. When installing over an FTP server, the installer connects first (to download base/hdlist and base/comp). Then it presents the list of packages, waits for the user to check which packages he/she wants -- then assumes the connection to the FTP server is still open. In reality, package selection may take a bit longer than 300 seconds (or even 900 seconds). At this point, the installer is unable to get even the first package, dies, and shuts down. Verified: just accepting the default package selection, the installation gets underway with no problems. Fix: disconnect before, and reconnect after, package selection to the ftp server
This should be fixed in the next release.