I know Japanese writing doesn't use spaces, but I understand it's value for the sake of beginners. The issue is that in the Kana Sentences test, when I write the answer in Romaji, once I hit enter, all the spaces in my answer get deleted, and my answer is counted as wrong. This happened several times.

Its not that it deletes the spaces but that you are probably typing something wrong. Make sure to verify that you are typing the correct letters.

I've noticed that there are some bugs though. On some cases, the correct answer says it should be a 'c' where a 'k' needs to be. Another common bug is with 's' and 'z.'