If you are viewing a chatroom's transcript, click the little arrow while you're hovering over a chat message. You will see "Star as interesting". This works for any date/time, regardless of how old the message is.
Now, try to unstar it. No effect. Why? Seems against all logic.
Take a look at this chat message from October 2010, for example. I starred it just now as a test, and now I cannot unstar it.
This has been fixed and applied as of build 307. (I don't think chat displays build information though, so it's hard to tell at a glance whether the changes have been deployed yet.)
Many thanks to rene for diagnosing this and making this an easy fix!
That is indeed a bug when you star/unstar from the transcript.
The endpoint that gets called is
https://chat.meta.stackexchange.com/messages/3784733/star
to star a question and the same call is made when you unstar it. The toggle of the message being starred by you or not is handled server side.
In the transcript however when you the click option 'Unstar' the XHR request goes to:
https://chat.meta.stackexchange.com/messages/3784733/unstar
which gives an error:
Status Code:404 Not Found
As a workaround without having to navigate back in the room you can unstar that message by excecuting this javascript from the developer console while you are in that chat room and logged in:
$.post('http://chat.stackoverflow.com/messages/1299/star', {fkey: fkey().fkey });
When you first want to experiment with that trick make sure to enter one of the sandbox rooms to not disturb the room with things that can go wrong.
unstar action is used for clearing all stars from a message, which is an action only a chat room owner can do (hence the 404).