Why can't i select more than one answer when it says 'check all that apply'?

In Teachable quiz questions where you are asked to 'check all that apply', it will seem as though you cannot click two answers. You choose the first correct answer, which turns pink and then grey, like the first image:

Then when you click the second answer, it will also turns pink and then grey. 

Both answers are now selected, and you can click 'Check'

You have chosen the correct answers and can continue on.

If this is not what is happening for you, then please send a screen shot if you can and a description of the problem to info@prekure.com.