Changing nick list settings not applying to all channels at once.

Join two or more channels.

Right click a channel name in the treeview
Click Nick list...
[check] Auto-hide nick list
[check] Set as default for all channels
Click OK

It only applies to the channel you right clicked and whenever you join/rejoin a channel.

Should this apply to all open channels instantly when changes? #msl (mIRC Scripting Language)