Comment by nathan-barry

Yes, this is the case. During training, the model will get a sequence of text (ex, 512 tokens long) with a percentage of them masked out (with a special <MASK> token). It learns how to unmask those tokens to construct the original text.

In the case that you mentioned, if we had 4 <MASK> tokens in a row, all we are doing for decoding is predicting what those 4 tokens should be.

Generally, this does not seem to be a significant problem, as there are usually multiple ways to express an idea in varying lengths. Also, with confidence-aware parallel decoding, it can usually avoid the scenario you mentioned, as focusing on decoding the highest confident tokens will generally avoid such scenarios with a well trained model.