Cannot select a certain word

There is a lesson where the word 答案 appears. It is white for me, so maybe I marked it as known before. But I wanted to look its translation up again, so I tried to select it, but the word cannot be selected. When I selected one more word left and right (的答案也), only a translation for 的 也 appeared.

Here is the link to the lesson with the phrase selected:

EDIT: Later in the same lesson there appears the word 方案 and this can’t be selected either. Interesting to note: It also contains the character 案.

Hi Leifa,
We are already familiar with this issue related to some Chinese words and we’ll try to fix it as soon as we can. Thanks for your patience.