I don't see any proof that your client is somehow not accepting IPv6 connections/preferring IPv4 connections or malfunctioning in any way. There aren't that many users with IPv6 on their connections (and I've definitely never had a node connected via IPv6, either on the different VPS services I used or in my home connection). The probability of having IPv4 nodes connected is pretty higher.

Here are Google's IPv6 statistics. They're worth what they're worth... but it's a starting point to measure adoption.