This question was closed as nonconstructive, which seems wrong to me. (The creator of the question also did not think it was right for it to be closed.) It's a question about a design decision (or else, about whether or not a particular behavior is a bug). Such questions have definite answers, even if the answers are hard to determine. Unless we're going to start closing questions for being hard to answer, it seems to me that questions about design decisions should be left open.

Some users' justification for the idea that this question should be closed was that the creator of the question can file a bug against the odd behavior, and then the response to the bug would answer the question. This is true for plenty of behaviors, but it is rarely an appropriate way to get support. For example, if I wanted to know why Libreoffice was written in Java, I could file a bug, "Libreoffice written in Java," in which I argue it should be written in some other language. In extreme cases, one could meaningfully say that an application is written in the wrong language and that a rewrite or code translation is warranted to fix the bug. But in those cases, one would be well-advised to consult with others first before filing the bug. In cases like the question linked above, it's not inappropriate to file the bug...but it's still better to consult with others first if there is doubt about whether or not the behavior really is a bug.

I'm concerned that by closing questions like this as nonconstructive, we're setting a precedent of encouraging potentially nonconstructive bug reports.

It seems to me that a better alternative would be to leave the question open. Then, if there are no good answers after a while, it would be reasonable to answer or comment, "No one has been able to provide a particularly good explanation for this behavior, strongly suggesting that it is a bug. You should consider filing a bug report about the behavior, and then the developers can decide if it is appropriate. They may also be able to provide an explanation for it. You could then use that explanation to write your own answer to your question."

Some questions about design decisions can be easily answered (like questions about why root logins are disabled by default, or why Libreoffice is included in recent versions of Ubuntu instead of OpenOffice.org). Those questions are never closed. I wonder if the desire to maintain a high accept rate on AskUbuntu subconsciously drives the practice of closing the harder questions about design decisions...