discrepancy in data volume in --perf and --file output from darshan-parser

Reported by Huong Luu:

The total_bytes field reported by darshan-parser --perf almost never agrees with the cumulative totals in the 2nd column of the statistics reported by --file (read_only, write_only, and read_write).

We should get an example log and investigate what causes this; it may be a bug.