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.