Last modified: 2013-08-08 13:33:09 UTC
CirrusSearch bases suggestions on all articles rather than those in the namespaces being searched because that is how elasticsearch is able to build a high speed suggester. It does make some of the suggestions pretty bad because they find few results.
I'm going to take a stab at fixing this problem by splitting our search index in half - articles in the content namespace go into one index and the rest go into another. This should mostly fix the problem because searches that just include content articles will only get suggestions from content articles. This has other performance advantages but I originally thought of it as a premature optimization but if it actually fixes the bug it'll be worth it for that alone.
https://gerrit.wikimedia.org/r/#/c/77821/