If you think you found a bug, or an error, it’s probably best that you just email it to firstname.lastname@example.org. But, if you don’t read this and post it in the forums please at least do it in the Bugs & Errors sub category.
Also, give us as much information as you can. Screenshots are a big help. Information on what browser, operating system, etc., is probably a good thing to do as well. Be descriptive, too. What were you doing when the bug occurred? Where did you find it? It’ll make it much easier to solve the problem.
The Bugs & Errors sub category is "public" in that content of this category can be found via outside search engines, even without a WaniKani account. Please don't post anything that you don't want the public to see associated with your WaniKani username.