In Settings > Search > Search Shortcuts, the help text currently reads "Choose the alternative search engines that appear below the address bar and search bar when you start to enter a keyword." This seems to imply that entering keywords into the search bar will bring up alternative search engines. However, this is not the case; only the address bar responds to Search Shortcut keywords, while entering keywords into the search bar will pass the entire string (including keyword) to whichever your default search engine was. Either the wording has to be modified to clarify that search engine keywords only work when typed into the address bar, or search keyword functionality has to be enabled on the search bar.