Here is the example I noticed recently (migrated to math.SE from mathematica.SE):
I was a little puzzled when I first saw this; of course, normally the user who has most recently edited or posted on the thread is listed next to the time, and even if that account is subsequently destroyed, the user listed as most recently participating is Community. However, it appears that when a question is migrated from a different site and whoever edited or posted most recently does not have an account on the new site, nothing is listed at all.
I'd like to suggest that next to the time (on the question list) either the user's name be displayed, but grayed-out, just like is currently done within the migrated post itself, or that Community be displayed.