I goofed in the post above, the development time should be the same as Xtol 1+0, not 1+3.
Now I just report that in a part full sealed bottle the developer is keeping well, at 52 days old its pH was 10.2 +/-0.1
Attached is a pic developed in it after 54 days.
The simplest explanation of what has been reported in the above posts:
Paracetamol/Tylenol is hydrolysed by the caustic sodium hydroxide (handle with care) producing p-aminophenol derivatives.
p-aminophenol is superadditive with ascorbate and regenerated by it,
ascorbate is oxidized to dehydroascorbic acid,
dehydroascorbic acid is orange,
dehydoascorbic acid is a stronger acid than ascorbic acid and tends to cause a fall in pH unless well buffered.
I don't think too much is public about ascorbate chemistry, it is post Film Developing Cookbook and other technical texts.