What is the issue with the HTML Standard?

During the firing of a successful download request navigate event, the navigation's ongoing navigate event is set. However, the ongoing navigate event is only later cleared in either the case of an aborted navigation or a same-document navigation, which download requests are not. This means that if two successful download request navigate events are fired in a row, the navigation's ongoing navigate event is null assertion will fail.

This case does not seem to have been covered by #11579.

This was discovered during the investigation of an issue reported in Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1994531

cc @noamr