Detect ip proto 48 [ipv6] ?

Why is there an IPv6 option protocol number appearing in an IPv4 packet?
Maybe it's just a bad packet.

Perhaps it's an IPv6 packet that has IPv4-embedded addresses, which is why
tcpdump prints IPv4 addresses rather than IPv6? I wouldn't think tcpdump's
printer could even try to find the presence of an IPv6 hop-by-hop option
in a true IPv4 packet.