In rP22856/D2264 the CreateGUIMessage function was reworked to consume arbitrary JS Values.
Before the commit, the "historic" property was always set, but with that commit it was only set for historic messages.
This works for chat messages ("historic": msg.historic lines in lobby.js`, but JS complains about an the property being undefined for the kick messages, and kicking is something I hadn't tested and may now pay with embarassment.

handleKick(false, msg.nick, msg.reason, msg.time, msg.historic);

The freezing should be performed for the copied historic message as well, because it is a new object, so the fact that its frozen was not transferred.

Join the lobby with two 0ad instances and a moderator account, have one of the players kicked, open the lobby dialog.
Consider whether it is cleaner to always define the property or whether it is cleaner to use the !!msg.historic cheat in JS.

The freezing can be tested by modifying the msg in lobby.js if historic = true, e.g.

		"room-message": msg => {
			if (msg.historic)
				msg.elexis = "stupid";