List of steps to reproduce (step by step, including full links if applicable):

1. Open a diff (example)
2. Select text in one column
3. Click anywhere on the page outside of the diff
4. Look at the data-selected-side attribute on the diff table

What happens?:
It remains "added" or "deleted" depending on what you selected at 2.

What should have happened instead?:
It should be unset.

The main issue that this can cause is that if at 3, instead of clicking, you start a new selection and get it inside the diff table, only one side will be selected. I'm not even sure if this can be considered a bug, but certainly it's not how things were supposed to work.