• Load VE on a page
• Switch to NWE
• Make some changes
• Click away (e.g. on the sidebar)

Expected outcome: OOUI message dialgo, "Are you sure?" / "Are you sure you want to leave editing mode without saving first?"

Worse but not-terrible outcome: Browser alert, "Do you want to leave this site?" / "Changes that you made may not be saved."

Actual outcome: No warning, browser follows link.

Switching to read mode by clicking "Read" from a changed VE, NWE, or NWE-switched-from-VE works.
Navigating away by click "Main page" from a changed VE or NWE does the latter.