In /includes/functions.php we have function short_ipv6(). It will expand a compressed IPv6 (i.e. from "FADE:BAD::" to "FADE:BAD:0000:0000:0000:0000:0000:0000" in order to be able to return as many words (hexadecatets) as requested.

However, the expansion will invalidate the address if it's one with an embedded IPv4, i.e. "FADE:BAD::192.168.0.1" will become "FADE:BAD:0000:0000:0000:0000:0000:0000:192.168.0.1".

The solution is to first check for an IPv4 and replace that with two appropriate words:
Find

function short_ipv6($ip, $length)

{

	if ($length < 1)

	{

		return '';

	}

After, add:

	// IPv6 with embedded IPv4

	$sOctet= '([0-9]{1,2}|[01][0-9]{2}|2[0-4][0-9]|25[0-5])';

	if( preg_match( "#$sOctet\\.$sOctet\\.$sOctet\\.$sOctet#", $ip, $aMatch ) ) {

		$sReplace= sprintf( '%02x%02x:%02x%02x', $aMatch[1], $aMatch[2], $aMatch[3], $aMatch[4] );

		$ip= str_replace( $aMatch[0], $sReplace, $ip );

	}

See http://tools.ietf.org/rfc/rfc6052.txt