I think I found a bug. It Occurs when using the dictionary page on Mac OS X (10.14.3) with with Safari (12.0.3) our Chrome (72.0.3626.119) and the IME that comes with Mac OS .
When I type in a hiragana string, the kanji picker menu pops up. I pick a kanji from the list and hit enter. The site comes up with searching but the text entry box reverts either to empty or to the last kanji entered.
Problem doesn’t exist on iOS safari using the stock iOS IME or when I copy paste a kanji into the search box on the Mac.