The form on Special:Search misses the “profile” hidden field in cases when it ought to have one.
If you open http://en.wikipedia.org/wiki/Special:Search?profile=help and try to search something, you will fall back to “Advanced”, which is probably not the behavior one wants.
Version: 1.20.x
Severity: major
URL: http://en.wikipedia.org/wiki/Special:Search?profile=help