opus-mt-en-zh does not respect the end token

Using the code here (but in c++): https://opennmt.net/CTranslate2/guides/opus_mt.html

auto translationOptions = ctranslate2::TranslationOptions();
translationOptions.beam_size = 1;
translationOptions.return_scores = false;

const std::vector<std::vector<std::string>> batch = {pieces};
const std::vector<ctranslate2::TranslationResult> results = translators[modelPathStr]->translate_batch(batch, translationOptions);

Translating something simple like "Hello", gives the chinese characters "你好" again and again (up to 256 times), which I believe is the max sequence length. Interestingly, translating "Hello, World!" gives the expected result.

Start with the linked Opus-MT guide and reproduce the C++ translation using "Hello" and "Hello, World!". Compare the generated sequences and inspect how end-token handling differs between the two inputs; done means the short input terminates at the end token instead of repeating until the maximum length.