/sockopen is not connection dependent and thus shouldn't have different behaviors depending on where it being called from. Currently, /sockopen will resolve based on the mode of the connection it is called from, this can (and in his case does) lead to unpredictable behaviors.
Where are you getting this behaviour from? I have IPv6 connections and calling /sockopen <hostname> or even /dns works fine to resolve ipv4 addresses on ipv4 hostnames.
"IPv6 mode" is a global mode, not server specific. You enable it by binding to an ipv6 adapter or enabling IPv6 priority. From then on, all /dns and /sockopen requests will use IPv6 first, regardless of active server connection. Try it yourself before "disagreeing". I use vyncke.org as a host that resolves in both ipv4 and ipv6.
Adding a -4/-6 switch works specifically because this is a global setting, and is specifically not a bug because you are enabling a global setting to prioritize a specific protocol over another. mIRC can't actually know what protocol to use until it attempts to dns the host, because it doesn't know if it's going to be getting an ipv6 or ipv4 address until the name resolves. You should be telling mIRC which one you want if you're going to be binding to a specific address (and specific protocol by extension).
