Blink, WebKit and Trident do not make use of the "sequential focus navigation starting point" when the :target is not focusable. Blink and Trident lose focus to body Because of that the tabbing sequence is reset to the beginning of the document when the browser is navigating to a fragment identifier. WebKit retains focus on the link, but that also yields a wrong behavior for the focus navigation sequence.

Click on "jump to target", then press Tab. Compare behavior with "jump to input" and "jump to focusable".