It has Ammounium Thiosulphate in it so there's no need to re-fix, as it's a pure metal ion substitution Selenium for Silver there's no Bromides or Chlorides present they were all removed in the original fixing step.

Clayne's point is more important about proper fixing and I suspect Logan's forgotten that Ansel Adams used a plain Hypo fixer before Selenium toning not after to make sure there was no staining etc from any quasi-soluble silver-thiosulphate intermediary compounds left in paper.

In addition the KRST is being used at a stronger than normal dilution for intensifying so any effects of the Ammonium Thiosulphate will be far greater, ie it's fixing action..

Ian