StackExchange [replaced the search engine a few months ago][1]. Among the many changes are how string and substring searches are handled.

>  - Quoted phrases are ***exact*** matches except for case-sensitivity, for example, [you can search for code][4] or [symbols][5].
>  - If not in a quoted phrase, words will now be stemmed ([example][6])

As @Iain said earlier, quoting matters.



  [1]: http://meta.stackexchange.com/questions/160100/a-new-search-engine-for-stack-exchange
  [5]: http://stackoverflow.com/search?q=%22*=%22
  [6]: https://meta.stackoverflow.com/search?q=stem%20test