I actually took that for granted because it's been a while since you can put the same address with the same group, so either it's not a new issue, or the issue always has been there.
Using $server($servertarget).group will potentially reveal one of the other groups besides the one you're actually connected to
$server() was never made or meant for you to deal with connected server, it's an identifier which allows to deal with the server list.
The servers list is old and was made for single connection, it's completely outdated and it's a shame mIRC hasn't improved in this area despite the countless features suggestions about it.
It is very anormal after all this time not to be able to automatically connect to multiple servers with specific nickname etc.
Anyway, this feature IS about connected server, and indeed it could be handy to access all these informations about connected server:
.name - same as $server itself
.ip - same as $serverip
.port - same as $port
.target - same as $servertarget
.targetport - returns full list of intended target ports (/server irc.server.com +5,*6 makes $server(1).targetport returns "+5,*6")
.group - returns the group that was matched if /server <group> were used and a group were found, it has nothing to do with matching the server name against the servers list ala $server()
.pass - returns the server password
.method - returns the auth method (related to /server -l)
.methodpass - returns the auth password
.ssl - returns $true if SSL is being used for the connection
.starttls - returns $true is connected to a STARTTLS capable server
.prevent - returns a combo of the letters 'p' 'f' 'o' 'c' corresponding to the /server switches
.desc is not applicable to connected server. I don't think the -46 switches of /server should have a property and possibly the -u switch could have a corresponding property but I don't know how applicable it is.