As the image above shows, even though the button highlight says I am on the "Words" dictionary section, in truth I am on the Kanji Dictionary, that's why めいずる is not found. This seems a display bug (Kanji should be highlighted instead of Words), to reproduce it is required speed using the mouse. Basically after clicking on a kanji during a quiz, the dictionary will be opened with the Kanji tab loading, if one is fast enough to click Words before the Kanji tabs finishes loading, then it will end up in the situation from the image above :) One non particularly attentive user might be tricked by this and end up thinking めいずる (or other common vocabs) are not part of this dictionary.