FP4 in Perceptol and Purple Stains

I've been having a lot of challenges with Ilford Perceptol developer.  Mostly I've used this developer with Ilford FP4 film.  I have also been using it with Bergger Panchro 400 and Rollei RPX-25.  The developer does not completely wash the anti-halation dye out of the film.  As a result there is a purple/blue stain left on the negative.  It varies from sheet to sheet within the same batch.  Sometimes it is very light and almost non-existent, while other times it is very distinct and obvious.  I'm hoping that for the most part I can print through this, and salvage the negatives.  But sometimes the stain is uneven, so this may not always be the case.

The problem is consistent through various manufacturing batches of the film.  As the problem is also evident in other films from other manufacturer's, it is obvious the issue is with the developer.

I've tried all sorts of things to attempt to narrow down the problem.  I tried processing the film without a water pre-soak, as Ilford recommends this.  That made no difference.  I was doing some reading online and it seems that others have had similar issues.  Someone suggested an afterbath [following fixing] in Dektol developer.  This is a very strong and robust developer and the theory was that it would wash out the stain.  It did not.  I normally use Perceptol diluted 1:1... so I tried a batch with stock solution and reduced development time.  This also made no difference.  My friend Arturo suggested trying some film that had never been frozen.  I generally keep all of my film in the freezer until I load it in film holders.  I bought a fresh box of film, loaded some, took some photographs with it, and processed the film.  There was little to no visible stain in any of the film that had not been frozen.  It seems that is the answer...!

But, this doesn't solve my problem.  I have hundreds of sheets of film in my freezer that I would like to use.  I can no longer consider using this with Perceptol developer, despite the fact that I very much like the soft look of the results.  I guess I'll have to buy a couple of boxes of FP4 and keep it unfrozen, for use with Perceptol.  The rest of my film I will need to use with some other developer.  Arturo suggested Rodinal would be a good choice as he is very happy with that combination.  That will be my next experiment.

The snapshot below is one of the sheets that showed the greatest amount of stain.  They weren't all this bad.  And when the film is wet, and catches some surface reflection, as this one is, the stain is much more evident.  But even after washing the film and drying it, the stain is still there.  I wash my film by soaking for 24 hours with at least ten water changes, after two rinses and a bath in Hypo Clearing Agent.  I rinse the film with distilled water before drying in a cabinet.