Launchpad displays This bug report is a duplicate of: blank / nothing sometimes

I first noticed this on https://bugs.launchpad.net/ubuntu/+source/evolution-data-server/+bug/1527495

It seems that bug has been recently marked as a duplicate of ubuntu / evolution-data-server bug #1279108 which I don't seem able to view, presumably because it is private or something (the annoyances of which are documented in other bugs elsewhere so I won't repeat them here). Launchpad seems to have an odd behaviour at this point, it is able to display the words "duplicate of bug #1279108" most places but at the top of the bug report just under the "Bug #1527495 reported by Thomas A. F. Thorne ..." message it states "This bug report is a duplicate of: " and that is all.

This was initially confusing to me as I wondered how the bug could be a duplicate of nothing? Once I scrolled down a read the comment posted by Apport https://bugs.launchpad.net/ubuntu/+source/evolution-data-server/+bug/1527495/comments/2 it made some more sense. Possibly the "duplicate of: <blank>" bit is caused by my not having sufficient permissions to view the bug.

Launchpad seems able to display a duplicate of bug #<number> most places I can access relating to #1527495 so I think it should also display the number in the message to give "This bug report is a duplicate of: Bug #1279108". As with any other links on the page I cannot follow a link or view details of Bug #1279108 but I would at least be able to see the data in the heading area and not be left confused about what is going on.

It is possible that this is problem with apport filling in fields correctly. However as most interfaces suggest the duplicate status and link to master bug has been set correctly I think it is more likely a weakness in Launchpad.

Attached image DuplicateOfNothing that shows the "This bug report is a duplicate of: " as it is displayed to me.