UPDATE March 11: The situation is becoming unbearable. Internally there's no way to find older questions, and I expect that this will invite lots of duplicate questions on the main sites.
If I ask a new question on TeX.se with the title "How to repeat top rows (column headings) on every page" then the system does not offer the question with the very same title in the "Questions that may already have your answer". I also can't find the question with searching for repeat top rows. A very similar question was asked today: How to continue table on multiple pages?. My only chance to find the possible duplicate was via a google search site:tex.stackexchange.com/questions long table with same heading on every page, the "Related" bar didn't help at all.
Please, please fix this soon!
UPDATE March 12: Hmm, it appears that the problem was fixed yesterday, which was very soon. A short official explanation would be nice so that my bounty isn't just lost
Original post below the line
This question was just asked on TeX.se: Command with variable number of arguments. I was sure that there was a very similar question before, so I tried to find it in the "Related" bar, but to no avail. Then I tried the search, e.g. with "number of arguments". Still nothing. Finally I managed to find it in the "Related" bar of another related question: The question I had been looking for (for at least 5 very intense minutes!) was A macro with variable number of arguments!!
How can this be? The question titles are almost the same, so why isn't the old question in the "Related" bar of the new one? And why don't I find it with the site's search functionality? Is this a bug?
Update March 7: That question I was looking for has another title now, and it has recent activity (which seems to be relevant), so let me give another example: Searching for encoding family is:question does not lead to my question How do I identify the encoding and family of a new math font? Why not?