In SequenceFileReader.Offset.increment(), line 204 overwrites currentRecord (a record counter) with newBytePosition (a byte offset), immediately after incrementing it on line 202:

  ++currentRecord;                        // line 202 — correct                                                                                                                                                                               
  prevRecordEndOffset = currRecordEndOffset; // line 203                                                                                                                                                                                      
  currentRecord = newBytePosition;         // line 204 — BUG: should be currRecordEndOffset

This is a copy-paste error: currentRecord should be currRecordEndOffset.

Impact

Every call to next() replaces the record counter with the reader's byte position. This corrupts:

• Offset equality/comparison — two offsets at the same record count compare as unequal if byte positions differ
• Offset serialization (toString()) — the persisted record= field contains a byte offset, not a record number
• Resume after restart — the HDFS spout uses the serialized offset to resume reading; a corrupted value causes records to be skipped or re-processed
• prevRecordEndOffset tracking — since currRecordEndOffset is never updated, prevRecordEndOffset always copies a stale value, breaking sync point calculation