Last modified: 2014-10-30 17:56:13 UTC
Edited posts do have two timestamps. On some edited posts the first timestamp always shows "[object Object]". On other edited posts the first timestamp appears to be correct but turns into "[object Object]" when hovering it. This can be seen live on https://www.mediawiki.org/wiki/Talk:Flow. Tested and confirmed with Firefox and Chrome, so probably not a browser issue.
Thanks for the bugreport and testing. This is a duplicate of bug 72170 - (the problem only appears for Topics that are loaded as part of the infinite scroll) - and will be fixed when they overhaul timestamps, which they're currently working on. *** This bug has been marked as a duplicate of bug 72170 ***