I noticed that when using the furigana in multiple choice answers, words that are made up of a Hiragana-Kanji-Pair are displayed wrongly. The Hiragana part just vanishes, leaving only the Kanji part. It is reproducible, below is a screenshot from a test schedule I created. いい人 becomes 人 in the multiple choice answers.
Hope this helps fix the bug, thanks for your efforts.
Edit: It seems to only happen with known Kanji, if there is furigana there will be hiragana, however if only the Kanji is displayed, the Hiragana vanishes, 大人になる becomes 大人, as a second example.
Edit 2: It seems to not affect Hiragana in between Kanji, in 通り越す, everything except す is displayed.