Database table columns for storing IP addresses have 40 characters only. The ideal IPv6 address can have a length of 8* 4+ 9 = 39 characters. However, RFC5952 section 5 clearly mentions that the last 32bit can be represented in octets style (IPv4), which means an IPv6 address can be expressed as...which has a length of 45 characters.
Currently IPv6 addresses with embedded IPv4 addresses are even recognized and accepted (in both 3.0.x and 3.1.x):But in the worst case the database tables just can't hold the longest form. Seems like up until today nobody ever encountered this scenario, tho.
Solution is to increase all IP address columns from 40 up to 45 characters.