TTL of A and AAAA records assigned to a FQDN

Today, I talked with some IT friends about the importance of having identical TTL of A and AAAA records assigned to a fully qualified domain name (FQDN). Take a look at the illustration below:

www.example.com. IN A 300 1.2.3.4
www.example.com. IN AAAA 100 2001:aaaa::1

In an resolver, the AAAA record will disappear in cache after 100 seconds. After that time, an IPv6 only host interrogates the resolver for www.example.com will only get the A records and the target site can not be reached. Similarly, in the case of TTL of AAAA > A, an IPv4 host can only get the AAAA records but due to the lack of IPv6 connectivity, the site can not be reached.

As a rule of thumb, TTL of A and AAAA records assigned to a FQDN must be equal.