Steps: 1. Open a tab with apple.com 2. Close it 3. Open another tab with webkit.org 4. Inspect <body> 5. Add "font-size: 12px" CSS property 6. Press Cmd-Z several times Expected: "font-size: 12px" is removed Actual: "font-size: 12px" is removed, then Safari restores webkit.org tab. Notes: Perhaps adding event.preventDefault() to keydown/keypress/input event can fix this.
<rdar://problem/90659656>
Bisecting showed that the bug was introduced by Bug 230351 - Web Inspector: Support fuzzy matching in CSS completions. I don't yet understand how.