The chat message history windows lack a title. To reproduce, visit http://chat.stackexchange.com/messages/5379827/history (or another message history page) and observe lack of title.
Yes; this is a bug.
message history | chat.stackexchange.comif you want something really short, or
"The message truncated to a reasonable len..." | history | chat.stackexchange.comfor a longer one.
(Lowercase for consistency with other Chat