This bug is very interesting. The subject isn't displayed because it ends with the subject of the parent message. See:
[screen shot of the mailman options for the address @n2.nabble.com for chandler-users f1653123]
[alternative location of screen shot of the mailman options for the address @n2.nabble.com for chandler-users f1653123]
The two bold parts are equal. When this case happens, Nabble assumes the second subject is pretty much the same as the parent one, plus some other irrelevant characters. The most common case is:
[Re: Re: Subject]
So we don't show subjects that end with the parent subject. I know that your case is a little bit different, but we must keep this algorithm generic enough to handle most languages. For example, "Re:" is "Res:" in portuguese. So we can't parse the sentence and try to discover if the chars are relevant or not. if you want that subject to show up, please change something at the end that will make it different from the parent subject.
Now: ignoring the fact that some of those documents are drafts and/or expired: recently I often cut the 'Re: ' from subject lines of replies. Nabble web UI behaves perfectly in this situation and happily, no complaints from SMTP recipients. I take the latter as a sign that:
* increasingly, people use mail readers that are properly designed to thread without total reliance on the subject line
Personally, I'm never shy of using a subject line that's specific, or long. A good subject line greatly increases the chances of things being rediscovered, and quickly understood, months or years after posting.
Looking ahead, wondering …
OT from Nabble, I wonder whether things like Google Wave will:
* increase subject line laziness
* make people less tolerant/understanding of good subject lines