[Bug-tar] misidentified tar.bz2 file

[sam]

I have a tar.bz2 file which will not open with the tar (1.27.1) command
tar -xf results_9694.tar.bz2
it gives the error:
tar: Archive contains ‘\002\200\0(\240(\240\n\0\0((’ where numeric off_t 
value expected
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous error

It was created with the command
tar -cvaf results_${process_number}.tar.bz2 run_files/result run_files/logs
On Scientific Linux release 6.2

I have ~20000 other files created with the same command that work fine.

It will open with
tar -jxf results_9694.tar.bz2
so it looks like it is being misidentified. Although 'file' gives the 
same result as any others:

results_9694.tar.bz2: bzip2 compressed data, block size = 900k
results_9695.tar.bz2: bzip2 compressed data, block size = 900k