John - Interesting experimental results.  Thanks for sharing those.

Your posting didn't say whether you ran dsmlabel or Label Libvolume on the J
tapes, or whether you took them as provided by the vendor.  I always label newly
introduced tapes, both to assure having correct labels, and to reset the 3590
VCR data, within your tape drive microcode level.  I'd recommend relabeling one
of those volumes and then test it.

  Richard Sims, http://people.bu.edu/rbs