I placed a unicode value of subscript 'a' (\u2090) in the key of a JSON file inside an object, and loaded it as document. This causes some values in the object, which are in the file after this key, to be read incorrectly, typically as null, but sometimes as undefined. The same applies when I put the unicode escape sequence in the key.

Interestingly, dumping the whole QJsonObject to qDebug() produces the expected output.

According to the JSON RFC, it occurs to me that the usage of this type of unicode character is valid in keys.