Pretty sure previous to 2216, an open tab for a file with unsaved changes was tagged with a bullet (like it is in the sidebar). After the upgrade, the sidebar maintains the bullet, but the tabs no longer do:
Can this get added back in?
FYI, this only seems to be the case in the Soda themes. The default theme shows a bullet instead of an "x" when the file is "dirty".
(Note that in my screenshot I mis-remembered where the bullet was. It replaces the "x".)
You need to add this to your preferences
I'm guessing it default to false since 2216. Don't know if it's intended or a bug, but in any case this setting will fix it for you.
It still works like that for me on 2215 (of which 2216 is a backport) without needing that configuration option in my user config file(s).