Comment 7 for bug 1292652

Utopic 161 still does this, though the symptoms are different and it usually only shows the black screen for about a second.

Once in a while though, it'll show for more like 20 seconds, complete with the blank entry in the app switcher, and often a crash afterward. Not a unity8 crash though, just the app.

Also related is Bug #1269841, which prevents the user from running the accounts app twice in the same boot.