I have a hero with 20 charisma have 11 in the command radius. I have a crown that give +4 to command radius and does not increase or decrease my current command radius when I take out or equip the crown.

After that I use a trainer to create a test character that have 60 charisma and have 19 in the command radius. The crown and banner that gives total +8 command radius does not increase or decrease the 19 in the command radius. I then make the character 20 charisma and have 11 command radius, the result is the same.

I make the character 6 charisma and have 7 command radius, now, equipping one or two + command radius items show a change the in command radius.

As such, at higher charisma point will invalid the + command radius items, is this a design to stop players from abusing the command radius too much? Many spells and convert building can be cast afar, too far for balance unless the character specifically invest in charisma that it is much weaker in intelligence and other stats.

Or it is just a bug that accidentally give a bit of balance to the game.

Are you checking this by using the "R" key and looking at the circle around your character? I think it doesn't dynamically update, so if you turn it off and on again, the new command radius will be shown.

Yes I did, do you encounter this in your game?

If you are talking about #3 this is my guess. I eventually used the patches linked in here to get rid of the multi-player balance stuff. I haven't seen how it works with regard to Command Radius but it wouldn't surprise me; some of those 'updates' really screwed with it.

As for #1 and #2 I only have really old versions and I've never played updated MP versions so I'm an idiot there.