As for why it relates to jails, it looks like the jail rc script was changed 2012/08/19 to allow ipv6 configuration to be set during startup. If you have actually removed ipv6 support from your system with the make.conf options, this doesn't work so the script fails and the jail doesn't start. The fix is to manually remove the ipv6 options from the jail scripts but ideally they should detect a lack of ipv6 (or ipv4) and adjust the start command automatically. (That or the jail executable itself should be adjusted to ignore ip4.* ip6.* options if the support isn't there).