Duplicate records dumped

[oowowaee]

My coworker and I ran into a situation today where we were dumping a model with 3500+ records to a file with
rake db:dump MODEL=MODEL_NAME EXCLUDE= FILE=OUT_FILE.

While the total number of records written to the file was correct, 300+ records were duplicated, and an equal number omitted. Setting the BATCH_SIZE to be > #total records fixed the issue.