Incorrect solution when the answer was correct

[JolonB]

I was using the LibreLingo website doing the Spanish course. At one stage, I got the task of translating "It's a horse". Using the options, I built the sentense "Es un caballo". Upon submitting, I was told that it was the incorrect solution, and that the correct one was "Es un caballo"... Huh? See the image below.

Later, during the same lesson, I got the task again. I entered the exact same answer, but this time it was correct.

To my memory, I did not do anything differently the first time I answered the question. I'm almost certain I just pressed the buttons in order without making any mistakes along the way. I have no idea what might've caused this issue, but hopefully someone here does.