Actually, it doesn't seem to have anything to do with the size of the project. I'm seeing this all the time now. Even after quit and re-open ST2, and open a small project. Rename a file, delete a file, add a file, none of it updates the sidebar.
I've noticed this often lately, too. I think it might happen when you have a large project open with a lot of files to keep track of? The only way I can fix it seems to be quit and restart ST2.
Customer support service by UserEcho