Ā and substitution with aa
The course tells me it's ok to use double vowels instead of accented ones. It works fine with one exception: When Ā is at the beginning of a sentence (no other long vowels have emerged at a word's beginning yet), it tells me I had a typo when I write aa or AA. It expects Aa while it usually doesn't care about capitalization.
It still counts the answer as correct, but it's annoying. If this can be fixed without much efford, it should be fixed.