When running mongoimport, there is a cap on the maximum size of a single object. It is set to 16MB, which would make sense if the limit applied to the size of the resulting BSON object (since that is our internal server limit), but it actually applies to the size of the JSON object being read by mongoimport. This results in situations where objects that would be a valid BSON object cannot be parsed. See example in "Steps to Reproduce".