Be careful when closing expanded stories in Pivotal Tracker
When you open up a story to only have a look at it, close it by pressing the "Cancel" button (or Esc key).
Clicking the arrow in the top left is the same as pressing the "Save" button. If someone changes the story description in the meantime you will overwrite their changes with everything you see, even if you did not change anything. If you only want to take a peek, prefer to hover the speech bubble icon.
If your story gets shotgunned and you notice it, you are lucky – and you may be able to get your changes back. Open up the history pane (Shift-H) and check the details link next to the "… edited this story" entries. You can not see label changes there.
This is annoying.