This is really a bug. The action was taken on a mac client, but afterward you cannot scroll back to previous messages before you used the /s command on any platform (windows, mac, mobile, web).

Repro steps:

1. In a HipChat room with existing messages, type in any emoticon and press enter. For example, "(coffee)"
2. Now replace it with 3 preceding spaces: "s/(coffee)/   (coffee)"
3. Do this about 20 times or so very quickly so it looks like the emoticon is moving across the screen.
4. Exit or close the HipChat application.
5. Reopen the HipChat application and try to scroll back in history before the emoticon message.
6. YOU CAN'T EVEN DO IT.