Possible bug? Phone number missing digits

Hi everyone! I’ve recently used Mockaroo to generate a comprehensive 1000 rows x 60 columns dataset. Upon subsequently validating the dataset I noticed that in a small number of occurrences (precisely 4 in ~1300) the phone number, which was specified in the ###-###-#### format, was missing the first three digits, e.g. looked like “-123-4567”. Has anyone noticed anything similar?