Reposting this issue in a new thread per moderator request with additional detail.
After initiating a manual upgrade to v3.9 on one of my sites, when I navigate to /wp-admin/edit.php?post_status=draft (which is normally how I get to my blog) and wait a second or two, my entire dashboard disappears. The entire left column goes solid black when this happens. The end site itself (what a visitor sees) appears unaffected and normal.
The dashboard seems to disappear only when I click on Posts in the dashboard. If I click any link other than one of the Posts links before the dashboard disappears, the dashboard stays where it should. For example, I can click on Media or Links or Comments and the dashboard stays visible. If I then click on Posts, it disappears after a second or two.
Very odd behavior.