It seems like there might be a couple of different threads on this subject and some bug reports. I've been doing some investigation from the perspective of a Journal Manager/Editor, whereas we a Web developer in our office who has been approaching this from a code standpoint. This is what my testing has produced.
I went through an issue I published today to try to match up the recorded publication dates with action dates in the history of each article record. Here’s what I found:
#72 publication date 3/24/2013. Same day, review assignment canceled
#82 publication date 3/3/13. Date submitted and editor assigned
#69 publication date 11/30/12. Date editor assigned
#73 publication date 3/24/13. No match
#74 publication date 2/24/13. No match
I believe that the setting of the publication date is most likely tied to when an article is assigned to an issue in the Editing page of an individual article record. It appears as though the publication date that is being set is what the date is at the time an article is assigned in the Editing page of an individual article (this action does not seem to be tracked in the history, so I can’t verify it).
This would seem to tie into the problem we are having when an issue publication date appears as null. I submitted articles with the QuickSubmit plugin on two sites. In both instances, I assigned an article to an issue while completing the QuickSubmit plugin and never in the individual article record on the Editing page. In both instances, the publication date then appeared as null on the Editing page of the article record and in the CrossRef export.
It seems to me that the action setting the publication date is associated with assigning an article to an issue in the article record. How the feature should work is that the timestamp when an issue is published becomes the default publication date everywhere. Then, editors can use the dropdown menu in the Issue Data section to override the publication date for an issue (which would trickle down to all article records) when necessary. In the case where various articles need to have different publication dates within an issue (such as the "publish as you go" journals), that publication date can be overridden in the individual article record's Editing page.
We'll continue to look into this issue here. It would be helpful to us if the person(s) who developed this new feature could point us to the commit file on the github (boy I hope I remembered to say that right) so that we know where to start our efforts.
If you have any questions please feel free to ask!
Electronic Publications Manager
Office of Scholarly Communication and Publishing
University Library System, University of Pittsburghvgabler@pitt.edu