I just noticed that a setting was added at some point to the new terms introduction page for vocab quizzes, which by default simplifies the displayed definitions. For users like me, who have simple definitions disabled, it makes no sense since the actual definitions quizzed will likely not match the ones on the introductory page. I think instead of having simple definitions on by default, the setting should match the user's setting for whether or not to show simple definitions.
It is only not matched because you have been around since before the update - I am pretty sure new users have simple defs on by default. You can toggle it off using the settings icon at the top of the intro page :)